I have a house on a slab that had a bathtub drain that had become disconnected for some reason, then the bathtub for 'x' years drained into the ground under the slab, which of course caused the slab to crack and subside. I got the slab mudjacked, which is marginally helpful. Slab has wire mesh on the bottom, no rebar inside it.
I thought the route I would have to take would be to have the pipe replaced leading from the bathtub drain to the main stack, which is about 6' away. In order to make sure that I knew where said pipe went, I rented a hammer drill and blew a hole in the slab about 8-9" across, right where the pipe should have been. Of course, it wasn't there. Then to prove my theory, I went over by the stack and dug another hole, and of course the bathtub pipe doesn't connect there at all. Apparently it connects more or less where the waste pipe leaves the house.
So in order to - as one replier suggested a few days ago - get at the drain under the tub, I made a third hole in the concrete slab, just to be able to get in there and work. I dug out the dirt and mudjack cr*p, and connected the tub to the original drain (which is an "S") and voila, the darn thing works like a charm. I just let the water run in the tub for half an hour, and there's no spills.
So but now I have three concrete holes. I think what I should do is fill them with sand, compress it as best I can, then mix up some industrial-strength concrete in a bucket and fill the holes. Does this make sense ?
If nothing else I hope you enjoy the story about someone who was so sure their theory was correct !