There is a smell in an interior bathroom with no windows. The tub is rarely used. When I noticed the smell, I got on my hands and knees to sniff everywhere, stuck my head in the toilet tank, shoved my nose in the tub drain, put my head in the vanity, and so on. Nothing smells up close, so I threw bleach down the sink, toilet and tub. Since the tub hasn't been run since I last cleaned it about 3-4 months ago, I figured that was the culprit. I ran hot water in the tub, cleaned it again for good measure, and thought the smell went away. That was when I noticed that the smell goes away when the AC is running. If there is no air being pumped in, the smell is there. That allowed me to rule out a dead critter in the duct work. Any ideas???? Thank you!!!