Periodically we have a strong odor that comes through the basement drain from the main sewer line. It only comes when we have our attic fan on that draws the odor up. It is so strong, it is embarrassing to have people over. We have had problems for several years, but it has gotten worse. I have tried pouring gallons of bleach and water down the drain to clean it, but it only helps temporarily. Any ideas what it could be?

This "basement drain". Is it a floor drain? A sink drain? Or something else? Cheers, Tom

Sounds like the trap seal may be evaperating over time. Is the flooe drain used or does it just set there? If it isn't being used then I would pour a quart or so of motor oil or antifreeze down there and see if the smell stops. Good luck, Tom