I've got a 1953 single story house with a basement. All the original drain plumbing is cast iron. We've been here about 3 years, and the drains are constantly backing up. Sometimes snaking a drain will open it back up for a while, without ever really pulling out much material.
Sometimes the drain refuses to start flowing again, and I end up taking things apart and it's always a trap or elbow that is filled solid with something black and very hard. I can't do more than scratch the surface with a screwdriver.
This picture shows an elbow that turned a stack as it went below the slab. It's chock-full of hard, black junk (with what appears to be a tiny hole, part of a channel where water was slowly draining):
I'm thinking this is most likely rust, although I'm not certain.
At this point, I've replaced a decent portion of the drain plumbing in the house with PVC, and I just had yet another drain back up (kitchen sink into the laundry tub below). I've already replaced that entire stack down to (and one elbow beneath) the slab.
Is the anything I can do to open these drains up besides replacing the pipe? I really am not looking forward to putting other projects on hold to cut up my slab again.