I would check for sewer gas leaks. Places where leaking gas from the waste system may present themselves are:
1) wax rings on the toilet.
2) either no water seal on the shower p-trap, or in worst cases, someone may have forgot to install a p-trap.
3) fill the p-trap on the lav.(sink)
4) Or, it could be any number of other problems, such as little critters getting in the walls and leaving little surprises behind. Maybe a pipe in the wall that was not attached. Any, Hey! Can anybody help me out here!
I hope this helps
: Mr. Love: I have a 2 year old home with a finished basement bathroom.
: It consists of a walk-in shower with floor drain, sink and toilet.
: I had the flush valve replaced by a plumber last Jan. because the toilet was mysteriously flushing
: in the middle of the night. Not long after, we noticed a strange smell in the bathroom. The shower
: hasn't been used except to flush water down to try to rid ourselves of the smell. Plumber suggested
: bleach, but that hasn't worked either. The smell seems worse lately. Is this sewer gas? What could be
: the sourse of the problem? Is there a "stink stack" connected to my basement bathroom plumbing? Might there be a problem there?
: It is really starting to bother us and get stronger!