for 3 days i have smelled sewer gas in my bathroom. i cannot tell if it’s coming from the tub or lavatory sink. as far as i can tell, there is not a leak at either trap. this house is 90 years old, so no codes = unusual plumbing design. nevertheless, we have lived here 5 years and this is the first time we’ve had this problem. by the way, the downstairs bathroom is divided so that the toilet is separate from the tub/lavatory, in its own little room. any ideas??