I have a store with a bathroom containing only a toilet and sink. No drain in the floor. There is an odor of sewer gas that comes and goes in the store area. Sometimes it is in the bathroom, but we can never pinpoint it. I inspected the bathroom but can't find the source. The base of the toilet is dry. The trap in the sink is filled with water. The stack pipe is covered by a plaster board wall all the way to the roof, so I can't readily inspect it, but there hasn't been any changes to the wall. Is it possible the wax seal on the toilet is leaking sewer gas but not water? Any ideas?