Hi,
I'm new to this website but find it very interesting. I have an old 2-story home in Chicago with a sewer odor in the upstairs bath. I'm pretty sure, after reading some of the posts, that the problem is coming from the roof vent(s).
Tom, your advice is awesome. Are you a licensed plumber? Do you live in Chicago? Would love to have someone who knows what he's talking about take care of this plumbing problem!! :)