I woke up this morning to find a strong smell of sewer gas in our basement. The smell is gone now. However, I do not know where the exact source is coming from. We had this same issue before with one of the pipes in our basement that runs through the floor and connects to the outgoing sewer line. At the time, the flooring around the pipe was cracked quite a bit, so we used concrete (the Quikcrete kind of stuff) to plug the opening. I was wondering if it was possible that the concrete is porous enough to permit the sewer gases to pass through it? According to wikipedia, sewer gases can consist of hydrogen sulfide, ammonia, methane, carbon dioxide, sulfur dioxide and nitrogen oxides--real healthy stuff :yuck:.