I have been noticing a smell from the upstairs bathroom for about 3 months now and didnt know what it was and now its seems to have crept in the bedroom . also have been noticing our cat likes to use the bathtub as his litter box. My husband has trouble smelling anyway so of course he cant smell anything. It all of a sudden hit me "SEWER GAS" . Do you think this is what I am smelling and is our cat giving me a sign by using the tub for his litter box cause he is smelling it too . Please help . thanks Roz