Your home has a drainage, waste and vent system (DWV) that removes sewage wastewater and prevents sewer gas from entering your home.
Sewage water flows from your home through a series of drain or waste pipes. To drain easily, a pipe needs an air supply (a vent) at the top. Look at your roof; you’ll see a large, round pipe that allows air into the system. A drainpipe is like a straw filled with water; the top of the straw must be open to allow water to drain.
Drain pipes are normally filled with air and – yuck – sewer gas. Each plumbing fixture has a P-shaped drain pipe beneath it. This sideways “P” stays full of water and prevents sewer gas from entering your home. If this water trap isn’t full, you’ll smell sewer gas in your home. A toilet has a different design: every flush drains the trap in the toilet bowl, and the trap refills as the toilet tank refills.
