I've got a sewer smell coming into my shower. I'm thinking it can only be a trap issue. Problem is the shower is on a slab. It's in the lower level of a tri-level house so it's half below ground level. Seems to stay away a few days after I run water again. The shower is pretty much not used. I've been here for 5 years and never had this issue. Is my trap underground really bad? Thanks
