My house was built in 1949 and remodeled in 2001. In the only original bathroom, a sewage smell started appearing several years ago every few months (this bathroom is rarely used). I used to just run water in the sink and bathtub and the smell would go away. Over the years, the smell started to increase to the point where it now appears daily and running water doesn't seem to make it go away. The wax seal has been replaced (the Roto Rooter plumber used 2 wax seals since the flange was tilted). The smell still comes back. He said the line seems to be OK since there's no gurgle or backup. What else could be causing the smell to get into the house? It's only coming from this bathroom, not the two new bathrooms added when the house was remodeled.

Help!