Standard pipe locating tools depend upon the pipe being a good conductor of electricity to permit a radio signal to be carried by the pipe. Using a proper radio receiver, the searcher can follow the strongest radio signal and locate the pipe. Plastic pipe will not carry a radio signal.
Several instruments have been developed based on putting a sound signal on the pipe at a point where access is available. Then using sensitive listening equipment such as water leak detectors, an investigator can follow the loudest noise and find the pipe. This works for pipes carrying water. Companies are investigating techniques for gas filled pipes but have not been successful to date.