Sewer Organisms
Another common source of smells is caused by the organisms that normally reside in the sewer; they can get to the house side of the toilet trap. They take up residence inside the rim of a toilet bowl (as well as the sink and tub overflows) and whenever the toilet is flushed, you will smell sewer gas. The problem most often occurs during hot and humid weather. The SOLUTION is to pour several cups of household bleach into the overflow pipe of the flush valve inside the tank. This will disinfect the rim of the bowl.