Plumbing Systems
Supply, pressure and shutoffs
Typical residential supply pressure is 40–80 psi; above roughly 80 psi a pressure-reducing valve is expected. Note the main shutoff, fixture stops and any cross-connections. A hose bibb or sink sprayer without a vacuum breaker is a backflow risk. Galvanized steel supply piping often shows reduced flow from interior corrosion.
Drain, waste and vent
Drain lines slope about 1/4 inch per foot for pipes 2½ inches and smaller, and about 1/8 inch per foot for 3 inches and larger - over 20 feet at 1/4 inch that is a 5-inch drop. Every fixture except a toilet needs a trap, and every trap needs a vent. S-traps, drum traps and spring-loaded "mechanical" traps are not acceptable substitutes for a proper vent. Report slow drains, gurgling, sewer odor, and any trap that is unvented or double-trapped.
Water heaters
The TPR valve must be present, unobstructed and piped in the same diameter as its outlet, flowing by gravity, ending not more than 6 inches above the floor or at the exterior, and never capped, plugged, threaded or fitted with a valve. A gas water heater in a garage is typically raised 18 inches unless it is a sealed-combustion or FVIR unit. Water at the base of the tank usually means the tank has failed.
Fixtures
Check the toilet flange and whether the toilet rocks (a sign of a failed wax ring), caulking at tubs and showers, and sump pump discharge that should carry water away from the foundation. Report visible leaks and corrosion; you are not certifying water-tightness.