I own a bungalow that was built in the mid 1970's. I purchased it almost 4 years ago. It has a basement suite that was there prior to my purchase. The problem that I have encountered is that there is an intermittent sewage type odor coming from the suite's toilet area. There doesn't appear to be a leak under the toilet and I had replaced the wax seal myself when I bought the place. The odor comes and goes and I was told that it could be a result of the stack being frozen. I could accept this, but then the odor should come from all three toilets and not just the basement one, right? If that is the problem, where would I find the stack and fix the problem. This is a regular sewer system and not a septic system.
Your concern may be caused by a separation in the vent stack plastic pipe within the wall of your bathroom. The movement in the wood frame during the hot and cold periods of the year cause expansion and contraction in your home forcing the pipe to separate within the wall allowing the sewer gas to leak into the wall area.