Help please! Recently bought a 90 y/o home. Every once in a while the basement smells like sewage. It is a finished basement, some mold on walls noted here and there. Nothing substantial. The smell gets worse the more laundry we do. We have two drains in the one end not finished, and I have poured multiple gallons of water/cleaner down them in order to make sure they are not dry. I have attempted to locate every vent down there and cap (if it does not make it all the way up). Have had a ton of rain here in western Pa this month and the place is dry as a bone. One day, no smell. The next, horrible. We have an interior french drain that appears to be fine, actually, no smell at all from there. What can we do??? It's driving me, and the wife, nuts. Thanks