Sewer gas

Hi guys,

My wife claims that when she washes dishes recently, that she can smell sewer gas in the basement. We live in the mdwest and have a catch basin. There is a bar sink, and laundry tub connected to the same sewer line, and there is also a floor drain in the basement next to the tub. What can be causing the gas to backup?

Thanks very much.

P.S. I have no sense of smell, so it's hard for me to figure out where it's coming from.

My uneducated guess is that something isn't properly vented and the trap is being sucked dry.

Tom