I recently purchased a home with a partially finished basement. The basement has a slight sewer gas odor that I've had trouble pinpointing but it does seem to be strongest in the bathroom which consists of a toilet, sink and shower stall. From a very close nasal inspection, the odor does not seem to be coming from the shower stall drain. The toilet has water in it so I'm assuming that would not be the source, which leaves the sink. I've heard that "S" traps can have problems and I'm not sure what one looks like but, the sink has a "P" trap. This is a spare bathroom ( there is a full bath on the first floor). The only thing I could think of is that the prior owner, an elderly woman, probably did not use this bathroom so it may not have been used for a very long time and the water seal in the trap simply dried up. Does that sound like a possibility? I ran the water to put water into the trap but I will not be back at the house for another week to see if it has made a difference. Could the water in the trap dry up in a weeks time? If this doesn't solve the problem, any suggestions for what to look at next?
George