A simple rule of thumb is that if you didn’t eat it or, drink it, it doesn’t belong in the sewer. The one exception is toilet paper and even then if you use a toilet paper such as the good old single ply toilet paper you have reduced your chances even further. There are very few sewer lines in perfect condition and most will have someplace such as a root that can catch the wrong items when they are flushed even the high quality soft but tough toilet paper can snag and start a build up that leads to a sewer backup. Things such as paper towels, baby wipes, tampons, sanitary pads, baby diapers, and even disposable bowl cleaning pads should never be flushed even though the manufacturer claims they can be flushed. I have yet to see the manufacturer of a “flushable item” step up to the plate and pay the cost of having a sewer snaked or, cover the damages from a backup into someone’s home. Never put grease down a drain as it will solidify somewhere in the line and build up over time causing a back up. If you are on a septic system make sure you have your system serviced with the tank pumped out at the required intervals. Avoid planting trees and large shrubs over your sewer line or, septic system. If you experience a back up and the drain cleaner suspects a line problem have the line camera inspected to see if there is a problem that can be fixed. If you have roots in your sewer line use Root-X once a year to control the root growth into you sewer line. All of these steps can help prevent a backup from occurring.
The most important thing you can do to minimize the damage once a backup occurs is to stop the flow of water into any drain. Even though the toilet on the third floor appears to work well if the main line to the sewer if blocked it will come up out of the lowest drain. To minimize damage other sources of water such as sump pumps, gutter drains, and storm drains should not tie to a sanitary sewer but should run to a storm sewer instead. If your sanitary sewer were to become blocked and it was during a rainstorm you would be at the mercy of the weather in having the flow of water into your clogged sewer controlled with every ounce of storm water or, ground water displacing sewage in the line into your home.
If the lowest drain or, cleanout opening in your home is below the level of the street in many cases you would be a candidate for a back water valve or, check valve to be installed on your sewer line. Clean Check is a good one that can easily be maintained from ground level through a cleanout plug. The backwater valve or check valve will close when the city sewer backs up preventing the water in the city sewer from backing up into your home. Of course you will not be able to drain water until the city sewer is cleared but at least you will be able to stop your neighbors from doing onto you. I believe the city sewer backups are the worst possible experience anyone could have. Customers that I have seen having a city sewer back up into their home were literally in tears wondering where all that water was coming from. In those situations a backwater valve would have been priceless.