I work for a foundation repair company and am interested knowing what methods are used to find plumbing distribution and waste lines under a slab. We will often cut a core in a slab to install helical piers that will raise and stabilize the foundation. Ocassionally we will hit a plumbing line and would like to avoid this problem.
Metal pipes are a breeze just use a metal detector to locate them however, plastic and polybute lines are a whole different game but can be located with a metal detector when the pipework is cut where it surfaces and a wire pushed through the line. Not always successful but in most cases it works just fine.
Selgas Services Ltd Craftsman Gasfitters, Plumbers, Electrical Service Technicians
There is one problem with the metal-detector solution, besides the situation where the pipes are non-metallic, and that is that many slabs contain metal wire/rebar, which confuses the detectors.
There is equipment that will detect the sound of water flowing through pipes. There is also a radar that can be used to get an image of what’s under the slab. There are specialized contractors who have this very expensive equipment, and I’ve seen both types used to locate hidden plumbing and rebar.