I have a semi-finished basement, and there is an odor of sewage in one room. That room has a sheetrocked ceiling and is below the guest bath. I saw no signs of water anywhere, so I made a couple of holes in the sheetrock (we're redoing the basement soon anyway) so I could get a look at the pipes. So far, I see one joint on the 3-4" cast pipe that may be the problem. The lead joint appears to be weak at the top, and there appears to be a dark, sticky residue from the top to bottom on the back side of the pipe which I can barely see, but no liquid on the ceiling underneath it. Does this sound like it could be the problem and if so, how would I temporarily seal it to see if it eliminates the odor? Thanks.

Does this sound like it could be the problem and if so, how would I temporarily seal it to see if it eliminates the odor?

Sounds like it to me. To seal the joint permanently the joint will have to be recaulked. This won't be as difficult as it sounds. You will not have to remove or pour a new lead and okum joint but you will have to rent or borrow a set of inside and outside caulking irons, (see image). Although I've put up a number of caulking irons the only ones you will use are numbers 4,(inside iron) and 5, (outside iron). If you decide to do the job yourself,( and you should since it's a five minute job) click on back once you get the irone and I'll walk you through the process of recaulking. Good luck, Tom

Thanks Tom! Something tells me though that I haven't truly honed in on the problem yet. I wrapped the joint last night with a little duct tape and a towel, and it didn't help immediately... almost got worse through this morning... was bad all day, then suddenly almost dissipated tonight!? However, I still smell it a little when I am walking to another part of the room. I've got a sneaking suspician something may have died in the ceiling, but it doesn't quite smell right for that. We had a mouse die a while back and the odor in one bedroom upstairs was different and lasted several weeks. I'm going to keep digging, and may unwrap the joint to see if smell comes back. Hard to figure out!