Code Library
Drains, Traps and Vents: Rules in Phoenix-Area Cities
Drain, waste and vent rules: slope, cleanouts, traps, venting, floor drains and storm drainage. City by city, then the Arizona law and model code behind it.
Uniform Plumbing Code
All UPC sections- Model Code · Updated Jul 2026UPC 1003: Which Fixture Traps Are Allowed (and Banned)UPC Section 1003 describes which fixture traps are approved and which are banned. The standard P-trap is allowed. S-traps, bell traps, drum traps, and traps with moving or hidden parts are prohibited. Each fixture gets one approved trap, and double-trapping is not allowed.
- Model Code · Updated Jul 2026UPC 705: Joints and Connections in Drainage PipingUPC Section 705 sets the approved ways to join drain, waste, and vent piping for each material. That includes solvent-welded ABS and PVC, no-hub cast iron, and soldered copper. It also bans joints that are prone to leak.
- Model Code · Updated Jul 2026UPC 706: Changes of Direction in Drainage PipingUPC Section 706 controls how a drain line turns corners. Every change of direction has to use an approved fitting with the right sweep. Tight fittings are only allowed where a horizontal line drops into a vertical stack. Turns that stay horizontal or flatten out at the base of a stack need gentle long-sweep fittings so waste keeps moving and does not clog.
- Model Code · Updated Jul 2026UPC 712: Testing Drain, Waste and Vent PipingUPC Section 712 requires new drain, waste, and vent piping to pass a leak test before the walls are closed. The plumber uses a water test with at least a 10-foot head of water, or an air test at 5 psi. The pipe must hold the test for 15 minutes with no leaks while the inspector watches.
- Model Code · Updated Jul 2026UPC 905: How Vent Pipes Must Be Graded and ConnectedUPC Section 905 sets how a vent pipe must slope and where it may tie back in. A vent has to grade back toward the drain so no water pools inside it, and it must reconnect above the flood level of the fixture so waste can never rise into a dry vent.
- Model Code · Updated Jul 2026UPC 907: Vent Stacks and Relief VentsUPC Section 907 sets when a tall or busy drainage stack needs its own vent stack and relief vents. A vent stack runs beside the soil stack to keep air pressure near normal, and relief vents cross-connect the two so falling water cannot pull trap seals dry on upper floors.
- Model Code · Updated Jul 2026UPC 908: Wet Venting a Bathroom GroupUPC Section 908 allows wet venting, a method where one drain pipe also vents the other fixtures in a bathroom group. The drain doubles as the vent for the upstream fixtures, so the group needs far less vent pipe.
- Model Code · Updated Jul 2026UPC 909: Island Fixture (Loop) VentingUPC Section 909.0 covers special venting for island fixtures like a kitchen island sink that has no wall behind it. The vent rises to drainboard height, loops over, and drops to a foot vent below the floor. A cleanout must be provided so the loop can be rodded clear.
- Model Code · Updated Jul 2026UPC 910: Combination Waste and Vent SystemsUPC Section 910 lets one oversized horizontal drain carry both the waste and the air for certain fixtures. It is used where a normal vent is hard to run, like a floor drain in the middle of a room or an island sink. The drain is sized larger than usual so air moves freely above the flowing water and vents the fixtures.
- Model Code · Updated Jul 2026UPC Floor Drain Requirements: Traps, Size, and Keeping the SealThe Uniform Plumbing Code requires a floor drain to have a trap, to be sized for the water it must carry, and to keep its trap seal so sewer gas cannot rise. Because floor drains sit unused for long stretches, code addresses drying-out with trap primers or approved seal devices.
- Model Code · Updated Jul 2026UPC Section 1101: Storm Drainage and Roof RunoffUPC Section 1101 governs how rainwater is carried off roofs and paved areas. It requires storm drainage to be kept fully separate from the sanitary sewer, and it sizes roof drains, gutters, and leaders based on the roof area and local rainfall so heavy rain drains without flooding.
- Model Code · Updated Jul 2026UPC Section 707: Where Drain Cleanouts Are RequiredUPC Section 707 requires access points, called cleanouts, on a building's drain system so a plumber can clear a clog. Code calls for cleanouts near where the drain leaves the house, at each long horizontal run, and at sharp changes of direction, sized to match the pipe.
- Model Code · Updated Jul 2026UPC Section 708: How Much Slope a Drain Pipe NeedsUPC Section 708 sets the minimum fall for a horizontal drain pipe so waste flows by gravity without clogging. Pipes 2.5 inches and smaller need at least 1/4 inch of slope per foot. Pipes 3 inches and larger may run at 1/8 inch per foot where the code official approves it.
- Model Code · Updated Jul 2026UPC Section 710: When Phoenix Code Requires a Backwater ValveUPC Section 710 requires a backwater valve on any drain line serving a fixture whose flood-level rim sits below the elevation of the next upstream public-sewer manhole cover. That valve blocks sewage from backing into the building when the main surcharges. Fixtures above that line must never drain through the valve.
- Model Code · Updated Jul 2026UPC Section 807: Indirect Waste and the Air BreakUPC Section 807 requires certain equipment, like a dishwasher, ice maker, or food-prep sink, to drain indirectly rather than being hard-piped to the sewer. The waste line ends above a receptor with an air gap or air break, so sewer water can never back up into food or clean equipment.
- Model Code · Updated Jul 2026UPC Section 906: Where a Plumbing Vent Can TerminateUPC Section 906 controls where a plumbing vent pipe can end so sewer gas leaves safely and cannot re-enter the building. A vent through the roof must rise a set height above the roof and stay a set distance from any door, window, or air intake.
- Model Code · Updated Jul 2026UPC Table 1002.2: Maximum Trap Arm Length by Pipe SizeUPC Table 1002.2 caps how far a fixture's trap can sit from its vent, so the vent can break suction before it siphons the trap seal dry. The limit rises with pipe size: 30 inches for 1-1/4 inch pipe up to 10 feet for 4 inch pipe. Self-siphoning fixtures like toilets are exempt.
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