check out the plumbing
Euph. to go to the bathroom. (The order is fixed.) I think I'd better check out the plumbing before we get on the highway.
greatest thing since indoor plumbing
and the greatest thing since sliced breadRur. the most wonderful invention or useful item in a long time. As far as I'm concerned, this new food processor is the greatest thing since indoor plumbing. Joe thinks Sally is the greatest thing since sliced bread. You can tell just by the way he looks at her.
visit the plumbing
Euph. to go to the bathroom. I think I'd better visit the plumbing before we go. I want you kids to visit the plumbing before we get in the car.