If you look under the sink in your bathroom, you probably will notice a bent pipe leading away from the sink and draining out either into the floor or the wall. This is called a p-trap and its main purpose is to keep sewer gas from leaking into your home. These pipes are attached to all plumbing fixtures in your home, and have been part of plumbing systems for a very long time.

Inside of the p-trap, water creates a seal that allows you to flush things down the pipe without any of the sewer gas making its way back into your home. This is important since sewer gas is harmful to your health, and naturally, it also smells really bad.

A p-trap can fail if the water sitting in the bend evaporates because the sink isn’t used regularly, and it could also be an issue if the pipe isn’t installed properly. A p-trap at the wrong angle might not have a water level that is high enough to block the flow of gas through the pipe.