The first thing you should do is try to locate the floor drain in your basement. In all probability it is in your utility room close to your hot water tank (but not always). You should then pour a bucket of cold water down this drain. This will fill the P-trap and create a seal that will prohibit those nasty sewar odors from entering the house at that point. Another good idea after you fill the P-trap with water is to pour a few tablespoons of mineral oil in the floor drain as well. This will float on top of the water greatly inhibibiting the evaporation process. If this solves the problem don’t forget that periodically you will have to replenish this trap with the addition of more water. Hopefully this will solve the problem for you. If not you should call a licensed plumber, who first hand should be able to troubleshoot your drinage and venting system. Good Luck.
Frank Hiebert
3rd yr apprentice
Edmonton, Alberta