I live in a first floor condo (formerly a two-family). There is a distinct "smell" (i.e., sewer-like) that only occurs when the bathroom window is open. It's worse on humid days. Over the past 4 years, I've spent several thousand dollars tearing apart the walls, having plumbers vent the drains properly, replaced the toilet seal twice, installed a ceiling fan to the outside and put silicon caulk around the base of the toilet. Nothing has worked. I'm at a loss about what to do next, as I've never had this problem anyplace else I've lived. ANY suggestions would be helpful before I spend more $$ (new toilet? checking if the main sewer pipe has a crack?) on things that won't work. Thanks!