Underground plumbing inspection occurs BEFORE slab pour. Inspector verifies: building drain size and slope (1/8 in/ft for 4in+), pipe material approved (cast iron, PVC, ABS per local), cleanout at base of each stack, fittings correct (no S-traps, proper sweeps for direction changes), DWV test (5 psi air or 10 ft water head for 15 min), stub locations match fixture plan, bedding material (gravel/sand) around pipes, no pipe damage, proper separation from water supply, pipe support at proper intervals. Common failures: wrong slope, missing cleanout, failed pressure test, pipe not properly supported, wrong fittings. HOLD POINT — no concrete until passed.