How do I find where the sewage smell is coming from? I know it is around the toilet. We just purchased our house in May...the seller said that we have all new plumbing. The smell is kind of a mystery...it doesn't happen only when you flush, or run water, or take a shower. We can be asleep and it will wake me up, it smells so strong and bad. It just happens no particulair time or anything. It also smells outside sometimes. But there are no visable leaks outside. It does make the grout in our bathroom tile discolored. How do I know if it is just a toilet and something we might be able to repair or if it is something I will have to call a plumber in and pay thousands of dollars for.

Mellisa and Ron Hogue, August 2006

The foul pipe system needs a vent to atmosphere.
Normally within roof space to external soil stack, opr you can have a AAV "Dergo valve" which normally sits next to the cistern above the bowl rim which allows air into the system but not out.
As the use of the foul drain causes pressure it may blow out water left in the traps which would normally seal away bad odours found in the pipes.

Paul, August 2009

You have a bad floor under the toilet.

WaxRingCrush, August 2006