Toilet, sink, and tub were roughed in about 5 weeks ago in basement; brand new pipes throughout basement. Sink, toilet, and tub are now fully installed. There has been a problem with drain flies from almost day one, as well as a sewer smell. We put a rag in the tub drain, and many fewer flies, but still a smell. Any suggestions? Are we going to need to rip apart the brand new bathroom walls and floors to figure this out?