The last two times it has rained, our basement has had a very strong odor, it seems to be a sewer smell. I checked in the crawl space where we have a hole that we drain our dehumidifier into it and that doesn't seem to smell. The water and toilets don't stink either. IT is a very overpowering smell that permeates even the second floor. Any idea what it could be? We have a septic tank behind our house about ten feet from the basement. The last time we had come home from someplace and couldn't figure out where it was coming from, eventually it went away.