Over the last few weeks I have been noticing a smell of sewer gas in my basement. The smell is not constant and comes and goes. I have noticed it more with the air conditioner running less. At first I thought the basement drain that the A/C drains into did not have the trap full. But when I put more water in it I could see it was full. The next evening the smell was present. Now I think the sewage smell seems to be coming from the basement drainage pipe itself. I think the smell is coming from the bottom of the pipe where it branches out. There is no water anywhere indicating a water leak out of the pipe. I dont hear any gurgling in the walls concerning the plumbing vent. What could be the problem here?? Does anyone have any ideas? All the other drains are regularly used keeping the traps full.

Installing a drain kit on an acrylic bathtub and have a couple questions: 1) I'm assuming that I don't need to use plumber's putty between the metal drain piece and the tub because there is a rubber washer/gasket supplied with the drain kit? 2) When installing the metal overflow piece, I placed the rubber gasket/washer on the back side of the tub and tightened the metal piece to the front side of the tub with the single philips screw. I am concerned about overtightening this screw because the metal piece has two small fingers on the bottom that rest against the tub and I don't want to crack the tub. How tight does the gasket, etc. need to be to ensure there are not leaks. I tightened quite a bit, but it seems like the gasket could be tighter. Am I doing something wrong here? Should I put a bead of silicone on the gasket before installing it to ensure a water tight connection?