Inside the home there are a number of places where the septic system odor could be coming from. The most common place is from a leaking wax ring under a toilet, this is the weakest joint in the entire DWV system and is the most likely joint to leak. If a toilet is loose and able to move or, rock the wax seal is compromised. It is also possible that the closet flange under the toilet may have not been installed properly especially if there has been a tile floor added since the closet flange was first installed. The height of the tiles sometimes makes it so the wax ring doesn’t even contact the toilet causing a place where sewer gases can leak into the home. Other places might be a drain that doesn’t have a trap installed or, one that is seldom used where the water has evaporated that was supposed to seal the trap keeping the sewer gases from coming through. There may be an air admittance valve or, cheater vent that has failed and is allowing gases to enter the home. Sometimes too there may be a vent pipe in a wall or attic that is broken or, maybe the plumber forgot to tie in when the home was being built. Sometimes too there are odors, which people thought were sewer gas odors but are not. A defective shower pan installation where the water stays pooling under the tile can smell pretty bad with all that swamp water under the tiles. Other times in the fall small critters such as field mice come in for the winter and die causing a odor. Finding the source of the odor can be tough enough without going the wrong direction thinking the odor is the septic system’s fault.
Sometimes if the odor hasn’t gone away in a couple of weeks like it would with a dead critter and no one has managed to find a leak you may need to do a smoke test. With a smoke test the known openings to the DWV system are plugged and a fan apparatus is hooked up to the vent with a smoke bomb blowing into the DWV system. The smoke will find its way to any leak in the DWV system and give you a visual indication of where the leak is that is allowing sewer gases to enter the home.