... ABS sewer pipe through or under a foundation? Any problems other than the work involved? What is the best way to seal the pipe if it goes through the foundation. Found some concrete compatible caulk at Home Depot... any good for this?

If it is a typical block foundation, just bash a big hole through the wall with a hammer, run the pipe, and then fill in around it with concrete. A poured foundation will be much more of a challenge. Accurately locate the spot on the wall where the pipe needs to go through. Rent a core drill and select a bit just larger than the pipe. A 4'' pipe should be 4 1/2'' OD. Measure before drilling the hole. Likely you would find a 5'' bit. Bolt the core drill to the wall where it is lined up correctly. You may need to rent a heavy hammer drill to drill a hole to bolt the core drill to the wall.

That concrete compatible caulk sounds like hype to me. Concrete may have hydrolyzed the old oil base caulk, but any acrylic or silicone caulk should be fine with concrete.

If it is a typical block foundation, just bash a big hole through the wall with a hammer, run the pipe, and then fill in around it with concrete. A poured foundation will be much more of a challenge. Accurately locate the spot on the wall where the pipe needs to go through. Rent a core drill and select a bit just larger than the pipe. A 4'' pipe should be 4 1/2'' OD. Measure before drilling the hole. Likely you would find a 5'' bit. Bolt the core drill to the wall where it is lined up correctly. You may need to rent a heavy hammer drill to drill a hole to bolt the core drill to the wall.

That concrete compatible caulk sounds like hype to me. Concrete may have hydrolyzed the old oil base caulk, but any acrylic or silicone caulk should be fine with concrete.
As it happens I just picked up a hammer drill...