Sewage has a natural tendency to produce odors. All sewers have some odors. The plumbing system in your home is designed to prevent these odors from entering the house. If you are experiencing odors indoors, it is likely that there is a problem with the vapor trap. Every water fixture in your house has a vapor trap.
All houses have plumbing vents that extend through the roof.
These vents allow air to flow both in and out of the house plumbing system, helping water to flow through the pipes. Working in combination with the vapor traps, gases from the sewer system are vented safely through the roof. When sewer gasses are present inside the home, it is usually the failure of one or more vapor traps. The water in a vapor trap will evaporate if the fixture is not used for an extended period. Seldom used bath rooms or utility sinks are commonly the source of sewer odors.