 The other thing that could be causing this, and sometimes this happens, is occasionally, and I don't want to freak you out, but occasionally you'll get a rodent that will die inside of a return duct. And if that happens, yeah, the stink can go on for quite a while. But I would take a look at that drain line, and if it doesn't have a trap in it, do that. And make sure it's filled with water when you start, if it's the winter, because it won't be. And I think you won't find any more air gets through that pipe. Sharon, thanks so much for calling us at 888-MONEYPIT.