Hi. I am in need of serious help. We bought our house 2 years ago as a new build. A few weeks ago, we started to finish the basement and had the rough plumbing put in for a 1/2 bath. Since then sometimes when I do laundry (laundry room on main floor) the basment fills with a strong sewer gas smell and if the furnace kicks on, the whole house smells. The plumbers have been her several times trying to figure out why but have had no luck. This never happened before we started finishing the basement. We have a whole house humidifier hooked to the furnace that was hooked to a little pump that sat on the floor but now they hooked it up to the sump. The sump lid has been sealed with silicone. They vented it through the main vent in the roof. Like I said, it doesn't happen all the time. The plumber said maybe it had to do with the way the wind was blowing at times so I've been trying to figure out if that has anything to do with it. And if so, how I'm supposed to fix it since I can't control the weather. The commode and sink are not installed yet. Would that have anything to do with it? If so, why does it only smell sometimes when I do laundry and not others. Any help would be greatly appreciated. Thanks.