Why Does My Sump Pump Smell?

When a sump pump smells the first thing that we need to do is determine whether it is a sump pump or sewage ejector pump that we are talking about. Many people do not know there is a difference between the two types of pumps yet the treatment for odor would be very different on the sump pump and sewage ejector pumps.

Sump pumps are used to pump relatively clean water such as storm water, or ground water that enters the sump pump pit. The pit may have a cover or it may be left uncovered. In most cases a sump pump will not smell or, may only have a somewhat musty smell. Sump pumps may discharge outside on the ground, into a storm sewer in most cases.

Sewage ejector pits are used to pump dirty water such as wastewater from sinks, tubs, showers, toilets and laundry lines that are located too low in a home to drain by a gravity drain up to a sewer line. The sewage ejector pits although they handle smelly waster still should not smell when properly installed and maintained. The pit should have a cover that is tightly sealed to the pit, with all pipes and wires coming up through the cover sealed to prevent sewer gases from leaking out of the pit and into your home. The sewage ejector pit should be vented through the roof and the waste from a sewage ejector only goes only to a sanitary sewer.

By now you have probably discovered that what you were calling a sump pump is indeed a sewage ejector pump. The things you want to look at when confronting an odor problem on a sewage ejector pit is the sealing of the cover and all the pipes and wires coming through the cover. The integrity of the cover and pit should also be examined. Sometimes older pits and covers were constructed out of steel, which has corroded and no longer is airtight. Other times gaskets are missing or, not properly installed. A vent through the roof is essential because the sewage ejector pit is so tightly sealed the air needs to be able to escape when waste enters the pit. A vent is required which goes out through the roof to allow the free flow of air in and out of the pit. Air admittance valves also known as Studor Vents or, cheater vents will not work in this application because they only allow the flow of air to go into the pit but not escape. The improperly vented ejector pit almost always smells as it is filled the pit pressurizes and air under pressure forces its way past seals that would not normally leak. Every thing on a sewage ejector pit needs to function properly to prevent odors from sewer gases from entering your home. If you have sewer gases from an ejector pit entering your home I would give a high priority to getting this problem addressed out of concern for the health of your family.

If you have a sump pump in many cases they are odor free with a good circulation of ground water and or, storm water that stays fresh via the circulation. In some cases during low water conditions the water in the pit may become stagnant. Sometimes it is as simple as running a hose into the pit for a little while to allow the pump to run a few cycles while other times you may want to put a loose cover on the pit. In most cases this is adequate for odor control. If you have water entering the pit that smells you want to examine if you have leakage in your sewer lines or, septic system if you have one which is allowing sewage water to enter the ground water reaching your sump pump pit. One of the ways that may check for sewage water to be entering a sump pump pit is to use dye to test the sewer lines. If the dye shows up in the pit you have leakage but it may not always show. Another way is to watch for water to suddenly start entering the pit when you drain water. If you have sewage leaking into the ground the leaking sewers should be addressed for the health and safety of your family and others in your neighborhood. In the worst case scenario you have smelly ground water entering the pit in which case you may just go to a sealed lid on the sump pump pit with venting to the outside.

Posted in plumbing questions, Sump Pumps & Sewage Ejectors Tagged with: ,
35 comments on “Why Does My Sump Pump Smell?
  1. bev says:

    I have a sewage ejector pit in my basement. When I had my house (built in 1902) lifted and a basement suite put in, I found that the suite plumbing (kitchen sink, bathtub, toilet, washer and sink in the suite and toilet, sink, shower and washer in my part of the basement). They all flow into the ejector pit. I have a kitchen sink on the first floor that gravity flows to the sewer line, and a second floor bathroom ( sink, toilet and bathtub) and these drain to the city line buy passing the sewage ejector pit.

    Everything drains fine but the problem is with the venting. When the sump pumps out sewage, it pulls the traps in the upstairs bathroom, the toilet bubbles and the water level goes way down, the bathtub and sink gurgle and needs to have water added 2 to 3 times a week. The entire house is vented though 1-2 inch pipe on the lower roof level. The plumbing was passed before the 2nd floor sink was installed, and when it was installed it was above the vent level so they used a Studor Vent, which is not code her in BC Canada. I am going to court and have found this entire process of leaning the plumping and sump needs interesting. I however have never been able to find trades people to supply estimates to correct this problem. I need to vent to sewage ejection pit on it’s own vent to the roof, I also need to vent the upstairs sink (at least) to the higher roof level to vent the sink.
    The house had a stack that ran outside the was and all vented well before I let the boozo contractor loose in my house. He used a vent to a 10 ft lower roof, and I can not even go on vacation without coming home to sewer gasses as the renters continue to use the basement plumbing in their suite and the pump pulls the taps in my 2nd floor bathroom.

    Now all I need is someone to return my calls, plumber, city, original plumber etc etc.

    Nice to vent mmm.. good word for this situation,

    • Redwood says:

      Hi Bev,

      I sorry to hear that your home is suffering from bad venting.

      You situation getting people involved is difficult. Many plumbers shy away from involvement both with repairing bad work and getting involved with the courts in cases involving bad plumbing. For a plumber to get involved with repairs to a bad system there is to some degree a fear of what they cannot see and assuming liability for that work. Testifying in court cases is also difficult because although the plumber may be an expert the subject they are testifying about may not be understood by the ones asking the questions and making judgment. It is also time consuming and keeps the plumber away from other work. To some degree there is a reluctance among plumbers to get involved with bashing another plumbers work.

      Your Lawyer should be able to find plumbers that specialize in being an expert witness for your case. You may also have to enter into an agreement with the plumber that does the repair work carefully spelling out what he is doing and what aspects of the work he is assuming liability for.

      Sadly the time for not having this problem is long past. Making sure that all work was done by licensed contractors and that all work done was done with permits and inspections, would have gone a long way in preventing the problem.

      I wish you luck in finding resolution,

  2. mackey says:

    Yes I live in Baltimore, MD this bad smell from the pump in the basement keeps coming back. We called a plumber and he said he’d check it out. He did and he says its normal, and to pour bleach in it to cure the smell. I disagree I think he’s not that big of a expert. I need a second opinion please heeeelppppp……..!!!!!!!!! This thing stinks

    • Redwood says:

      Hi Mackey,

      Is this a sump pump or, a sewage ejector pump?
      Is it covered and sealed or, open?
      Does this pit have any waste water going to it or, is it only ground water?


  3. John says:

    I’ll start out by saying that what I have is a Sump Pump, partly because of what I’ve read in blogs and because the previous owner of our home, who installed the kit, left a box for the unit that says “Sump Pump” on it. It is a square hole in the ground that is covered with a steel lid that has holes in it, so that if there is a flood in the basement the water will drain into the pit. There is a nasty smell that comes from the pit, very much like sewage. Pouring water into the pit addresses the smell but only temporarily. Most recently I tried covering the lid with a garbage bag and sealing the perimeter with water vapour tape. This has addressed the smell completely, but the plastic bag rises slightly as if it were trapping gas that is trying to escape from the pit. Plus, the bag doesn’t look so great.
    Is there any danger in what I’m doing? Is there a better solution?

    Many thanks for any help that you may be able to provide.

    • Redwood says:

      Hi John,
      I would check to see if there are any sanitary drains feeding into the pit.
      There shouldn’t be any going into it.

      There is a possibility that you have a sanitary sewer leaking into the ground water that is causing the smell.

      Sealing it may only be covering up a problem and in some cases could interfere with the flow of water into the pit.


  4. John says:

    Hi Redwood
    Thank you for your reply.

    There doesn’t ever appear to be any liquid leaking into the pit….but I did discover an extra piece in the Sump Pump box that got me
    Thinking. It is called a back flow preventer – but it doesn’t look like the ones I’ve googled. It is a rubber circular piece with a screw coming out the middle. The rubber piece pulls up and creates a kind of seal with a brass circular “connector” that screws onto a 3″ drain There is one installed on the sump pump already….but there is a gap between the rubber and the brass. I wonder if ihe rubber is not pushing up enough and leaving a gap for odors to escape? Should I replace this piece?
    I’m also going to try filling the pit with water/bleach to get the pump working before replacing this back flow preventor…

  5. John says:

    Hi Redwood
    I emailed you a couple shots earlier today. I hope it is helpful.
    Thank You!

    • Redwood says:

      Hi John,

      Thanks for sending the picture I know what we have going on now sort of anyway.

      Floor drain check valve

      This type of device is typically used in a floor drain to prevent sewage from backing up into a basement in the event a main sewer line clogs or the city sewer backs up. I would not consider them something that would seal well enough to prevent odors, usually these are used on a floor drain that has a trap to stop odors. If you notice in the picture it is slightly open, I don’t know if you are holding it open or, it just naturally is open but it will not stop odors effectively.

      Seeing this device in your sump pit makes me wonder if your sump pit in addition to the pump also has a drain in the pit with the pump as a backup. If this is a drain and it goes to a sanitary sewer the drain may be either clogged and be spilling sewage into the pit or, not have a trap which could be the source of your odors.

      Another picture of the inside of the pit may give enough information to determine if those problems exist.


  6. John says:

    Hi Redwood
    Thank You for helping me identify the problem. It appears as though the smell is in fact coming from the drain and the sump pump is merely tied in as a back up unit in the event of a flood. As for the drain, there is a trap, but the drain spilts into two directions below the floor (it’s fully visible in the pit)…..kind of like a cross, with one arm lower than the other. On the higher side the drain runs straight to the east. No trap. On the lower arm there is a trap with a drain running west. At first it looked like the trap might be dry because water rarely sees this drain. But then I remembered that a kitchen sink in the basement drains straight into this unit – and we have tenants that use it regularly. So perhaps the line that runs east has no trap and is the source of the smell. I will see about putting a trap….but will cover the pit in the meantime. Redwood, you’ve gone above and beyond in helping diagnose the problem and I am in your debt.

    Thank You
    John T

    • Redwood says:

      Hi John,

      If the tenants kitchen sink drains into the pit then a different type of pit is needed.
      With sanitary waste the pits are enclosed and sealed to prevent the sewer gases from escaping.
      They also are vented through the roof.

      If I’ve mist understood what you were saying and only the drain is used then there isn’t a problem with that.


      • Yourcalling says:

        Hi Redwood,

        Did you mention that food from a basement kitchen sink should not go into the sewage ejector pit but another pit is needed? If so, what is needed for food from a basement kitchen sink to get out into the septic line/tank?


        • Redwood says:

          Hi YourCalling,
          The kitchen sink may drain to a sewage ejector pit but may not drain to a sump pump pit.
          There is a difference and when they get confused ugly smells may result.

  7. John says:

    Hi Redwood,
    Sorry, I should have been more specific. The kitchen sink runs into the drain directly….so there should always be water in the trap. I’m assuming the odors are coming from the east ‘arm’ of the drain where there doesn’t appear to be a trap. Should both sides of the drain have a trap?

    • Redwood says:

      Hi John.
      The only opening in a drain waste vent system that should be open to air without a trap is a vent through the roof.
      So any drain out of that pit should be trapped.

  8. Melissa says:

    After reading the article regarding odors from Sump Pump, I have learned that I actually have a sewage ejector pump. I live in a split level home and our pump is in the garage. There are certain times of the year, possibly after a rain and drying up is occuring outside, we notice a foul odor throughout our garage and home. What should we do to correct this problem. Embarassing to have this odor.
    Thank you in advance for your advice.


  9. margie gipson says:

    I just moved to a community in Oak park Mich. I noticed dried toliet paper around the furnace drain pipe as well as dried fetices on the bottom of some cabites in the basement. The basement also smells really strong of sewage. The waste had been painted over instead of cleaned. I called maintance and they scraped the painted foor area and wiped down the cabinets. Nothing more!! There is also a wooden box screwed down to the floor (about a half inch from the floor). They told me it was a slump pump. But I think that it is a sewage injection pump. There is a four foot white plastic pipe connected to the laundry tub and floor drain vented with a miniture studor vent. during the night I hear the toiets running as if some one is using them, I have to flush them to stop the water from running. I tried to sanitize the basement layndry room area were the smell is really strong. My grand children was palaying on the other side of the basement.Two days later i came down with a serious infection in my large bronco tubes (cronic broncitis)I still have it a month later after taking antibiotics. My grand children also were vomiting a couple of days later and my grand son even fainted. Please give me some much needed advise. P.S. I am renting.

    • Redwood says:

      Hi Margie,
      It sounds like your home has a few problems. The sewage system has obviously backed up into the basement and was never properly cleaned up and sanitized after that event. The evidence of the dried toilet paper and feces wouldn’t be there if a proper cleaning had been done and painting over the stain in no way is sufficient cleaning. On that basis alone you should be contacting your landlord to have the basement cleaned properly, and if there is no action, contacting health officials. If the toilet paper around the drain is ever wet or, new waste appears that is evidence that the sewer is backing up and needs to be cleaned.

      As far as the odors there also much concern as well because it sounds like you are getting sewer gases coming into your home and these gases can indeed cause the health problems that you indicate the children are having. The problem may be as simple as the floor drain by the furnace having a trap that has dried out so there is no longer water in the trap which prevents the gases from getting in through the drain or, it may be more complex such as a sewage pump that is not properly installed or, even drain pipes that are defective allowing the gases to leak in to your home. It sounds like the maintenance staff is either not concerned about the problem or, is not capable of diagnosing how the sewer gases are entering your home.

      The landlord needs to call in a good licensed plumber that can look into whether or, not the “Sump Pump” is indeed receiving sewage waste, and to check for other causes that would allow sewer gases to enter your home. The testing the plumber performs may include a visual inspection for defects, tracking waste flows with dye, a peppermint test to indicate a compromised drain waste vent system, and smoke testing to indicate where the leakage of sewer gases into your home is coming from. In any case you have problems which must be resolved for the health and safety of you and your family. What level of action you need to take depends on the landlords desire to take action and I wish you luck.


  10. John Canfield says:

    Hello. I have 2 sump pump pits and one ejector pit. I have an odor coming from one of the sump pump pits. The pit with the odor is the pit that the cloths washer drains into. This pit pumps directly into the sewer system. The pit has a lid but is not sealed. Should the cloths washer drain into the ejector pit instead of a normal sump pump pit? Also, all 3 pits are joined by an overflow pipe, that pipe from the ejector pit to the sump pit should be sealed, correct? Thanks!

    • Redwood says:

      Hi John,
      It sounds like you may have several problems which will probably need to be sorted out.

      The sump the clothes washer drains into does need to be a sealed, vented, pit and would be a sewer ejector. The discharge from the pit is grey water and needs to go to a sanitary sewer.

      The other sump pump are ground water which should if it goes to a sewer in many areas would be required to go to a storm sewer. Check your local requirements.

      A pit containing sewage or, grey water should never connect by any means including an overflow pipe to a sump pump that is handling ground water.

      I hope this clears things up for you,

  11. Lisa W. says:

    Hi Redwood,
    I have a sump pump pit in my basement which my husband and I dug ourselves about 5 or 6 years ago. There are absolutely no sewage connections. It is a simple, single square pit with a sump liner and a pump. Water in the pit is pumped up nearly to the level of the basement ceiling and out of the house through the wall. There are no sewer lines in my rural area, and the pit is on the opposite side of the house from our septic system.

    For the first few years after digging the pit and installing the pump, we had no problem at all. Last winter, we began to smell a sulfurous stink from the pit that got stronger when the weather/ground was dryer. It can be smelled in various parts of our home, especially in the bathroom above the pit location. Using bleach in the pit only decreased the problem for a few days and did not seem to be a solution. The problem corrected itself in the spring, and there was no odor during the summer. It is now nearing Thanksgiving, and I have noticed the odor recurring and getting worse over the last couple of weeks. Other than a single dehumidifier (used only in summer), nothing but ground water should be draining into this pit.

    Do I need to have a septic company check it for septic backup? Or is it likely to be a simpler problem of drying water getting funky in the pit? Is there an enzyme product I can add to the pit that will eat the organic matter without damaging my pump? Since it only stinks in the winter, am I wrong to think it isn’t likely septic contamination (which should be obvious all year, right?) I’m looking forward to whatever advice you can offer.


    • Redwood says:

      Hi Lisa,
      It sounds like you aren’t having sewage contamination and more likely the odor is either a sulfur or, iron reducing bacteria. You may have some luck pouring a sterilizing bleach mixture into the pit, but I think a cover installed on the pit would probably be the best solution. As you stated the bleach was only temporary so a cover to contain the odor is probably the best solution. Bleach use over the long term may cause deterioration of plastic and rubber pump parts as well as corrosion of metal parts.

  12. Dawn says:

    We need help. we have had a sewer smell for 2 months in our home and tried everything to find the problem. We finally were relieved to find where it was coming from but now do not know what to do. It is coming from our sump pump pit. It only happens when we run hot water and would only fill through the house when the furnace is on. The furnace is next to the pit so it is obviously pulling the smell and spreading it through the house. My husband covered and sealed the pit and it fixed the smell in the house. But now we are nervous on if this is safe and why is there this smell. It smells like methane gas. We have a septic tank and just had it pumped out since we though that was the problem and it was not. We do not know if we should just keep it sealed and go on with our business. This seems unsafe. We have had plumbers, drain people, and contractors out and no answers. Help us… Thanks!

    • Redwood says:

      Hi Dawn,
      The first thing I would do is check to make sure that the only water going into the sump pump pit is rainwater, stormwater, or, groundwater. If any water goes into the sump pump pit from sinks, showers, washing machines, etc. these should be rerouted to the septic line. I would also check to see if any drain lines can be leaking waste water into the sump pump pit. Do any of the drain lines run under the basement floor where they might be leaking underground into the sump pump pit? The ground water may have a high sulfur or high iron content which can lead to the colonization of sulfur reducing bacteria or iron reducing bacteria both of which may cause odors. You may be able to temporarily sanitize the pit by adding chlorine bleach to the water in the pit and see if that kills the odor, a 10% solution will sanitize the water.

      The fact that you say the smell happens when you run hot water has me wondering about the possibility of a drain leaking into the pit. The hot water use coinciding with the odor also makes me wonder if there might be a bacterial infestation in the water heater tank. Many times when your water supply has a high sulfur content a Sulfur Reducing Bacteria colony will develop in a water heater tank and will give off a rotten egg smell when hot water is used. The furnace will then spread the odor through the home.

      Does the furnace have a condensate drain going from the air handler to the sump pump pit or, sanitary drain line? If the condensate line does not have a trap or the trap has dried out, air from where the condensate drain goes to can be drawn through the condensate drain into the air handler where it is then distributed through the home.

      It is hard to diagnose this without being there to check it out for myself. These are all possibilities which I would examine when chasing down an odor, attempting to remeditate the problem. It’s weird that I developed a good track record of solving odor problems, because I have a nose which works very poorly and the odor has to be very severe before I’ll even smell it. But my success is from checking all the possible causes rather than sniffing around looking for the source.

      I hope this helps, let me know if you have any additional information,

      • Dawn says:

        Thanks so much for the reply. We cleaned the pit as you suggested but the horrible smell is still there. Its unbearable and only when we use the hot water. My husband totally air sealed the pit which fixes the problem but we feel as if this is unsafe. The smell has to be a sewer gas and could be explosive. This made me nervous but after spending crazy amount of money on plumbers, sewer root people and the septic pumped and still no answers we resorted to sealing it. We need to find out the problem and fix it. We need to figure this crazy smell out. I am nervous it may be a drain line which would be very pricey to fix. Our house is a very old farmhouse 1870, so nothing is easy to repair here.

  13. jeremy says:

    Hello all I have had this bad smell for 2 years now from my sump pit and I found the easy fix to stopping the smell.. I drop a chlorine puck in (the same kind that you would put in a swimming pool) every month or so… This has gotten rid of the smell completely… Hope my discovery helps other people.. Your welcome from Jeremy in Ontario.

    • Redwood says:

      Hi Jeremy,
      Thanks for your comment this is a method used by many people, but it is one that should be avoided. The disinfection of the pit using bleach in small quantities which I stated provides temporary relief is more of a diagnostic tool to temporarily remove the smell from the pit. The problem is that the groundwater is actually an underground river that is quite large and constantly moving so the amount of water present is larger than you imagine. In essence your chlorine puck is trying to disinfect the entire river and is actually contaminating the aquifer with chlorine. For this reason even backwash water or, water drained from swimming pools is a regulated discharge in many areas with the chlorine level required to be as low as 1 ppm or, less. In addition the high concentrate of chlorine in the pit will be corrosive to the metal parts and degrade plastic and rubber parts of the sump pump contributing to an early failure of the pump.

      For these reasons I do not recommend the practice of using pool chemicals for long term disinfecting of sump pump pits. Instead I would recommend the practice of installing a sealed and vented pit cover similar to the ones used for an sewage ejector pit or, radon mitigation in order to eliminate the smell. One other thing I should note is that the sulfur, and iron reducing bacteria is harmless, and is just a nuisance.

      Thanks for mentioning this and bringing it into the discussion,

  14. Karen says:

    My Mother has been experiencing this above mentioned smell for quite some time. I’ve recently learned that my brother who lives in the basement has been URINATING in the uncovered sump pump.It’s located next to the washer as well,if that makes a difference.Of learning of his disturbing habit,I fear that he may be doing more than just urinating. But even if it was just urine,could that be the reason or contribute to the stinking problem? Please help. I am SO nervous for my Mother to be inhaling this on a regular basis.

    • Redwood says:

      Hi Karen,
      Sorry to hear of your brother’s lazy bathroom habits. This would certainly be a contributing factor to odor coming from the sump pump and if your brother was putting anything else in the sump you would see evidence remaining.

      The next to the washing machine may be something. If the washing machine or anything else other than ground water is draining into the pit then it would be grey water and should drain into a sealed pit which is vented through the roof.

      For now lets get your brother cleaning up his mess and getting the pit so it doesn’t smell. Time for some garden hose work!

      Hope this helps,

  15. LScott says:

    If this is the problem is the sewer ejector pit would this cause the odor to come up through the hvac whenever its turned on during the winter or summer. If you have a odor problem in the home could the heat pump be apart of the problem? Also, the heat pump can cause the odor to be moved through the venting system in the home?

    We had the crawl space sprayed. The crawl space was encaptulated. The outside water spouts were tested and fixed if there was a problem with them. We never had the odor smell when we had a gas heater in the home. Whenever it rains, you can smell the odor. We had a plumber come and view everything and he implied that there is no problem. At some point around the outside of the home you can smell the odor. Individuals from the city sewer department came out and could not find the problem. They indicated that the sewer system was working fine. Still the odor problem exist. Could the sewer ejector pit be the culprit behind the problem? What are your thoughts and recommended solution?

    • Redwood says:

      Hi LScott,
      If the HVAC System is suspected as an odor source, which is definitely a possibility, I would examine the condensate drain as the most likely cross connection. If the condensate drain is connected to the sanitary drains of the house, in seasons where the system is not making condensate the trap on the condensate drain may dry out allowing sewer gases to be drawn into the HVAC System and distributed throughout the home. If the condensate drain is connected to the sanitary drains of the house then the odor will be drawn in all of the time.

      For this reason many mechanical codes prohibit HVAC condensate drains to be connected in this manner. If your drain is connected in this manner consult with your local building inspector to see what methods are allowed under your local building code.


  16. Brandon Kula says:

    After reading this great article, I’ve learned I have an ejector pump in my basement. The pit smells from time to time when the washing machine drains into it. The only things that go into this drain are the washing machine and a utility sink, and they do go into a sanitary sewer line. When I purchased the house the pit wasn’t sealed, and still isn’t. I know very well this is where the smell comes from, and from reading this article that it should be sealed up and vented. Being that my home is older and 2 stories, it will be very difficult to run a vent to the roof. Would it be acceptable to run the vent outside, and then up above the roof line? Also, any advice on the best way to seal the pit? The motor and float switch stick up out of the pump, and I’m not sure how I would seal this off and still allow the float arm to move up and down to activate the switch?

    • Redwood says:

      Hi Brandon,
      The proper sealed pit and submersible pump along with proper venting will need to be installed. Based on your description nothing there will be usable.

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