Sewage has a natural tendency to produce odors; all sewers have odors. The plumbing system in your home is designed to prevent these odors from entering the house by using a vapor trap. If you are experiencing odors indoors, it is likely that there is a problem with the vapor trap. If you experience a problem with your vapor trap, a plumber can help you.
Atmospheric conditions can also affect odors from sewer systems entering the house. When barometric pressure is falling or is very low, the air outside can be heavier than air from the sewer system, causing pressure to build up in the sewer system. This temporary condition may cause indoor odors, but will resolve as barometric pressure increases.