Remodeling bathroom and disconnected toilet, sink, and replaced tub rough plumbing before P-trap to fit shower drain. Tested shower drain and no leaks. Everything has been disconnected maybe 3-4 months. We keep getting recurrent sewage smells, so we flush the drains with water to get the trap sealed again. But the stench comes back closer and closer together. First it was several weeks, than two weeks, now it seems to be every few days. Thoughts?