Free Plumber Practice Test

✓ Correct Answer: 4 DFU

Under the IPC (Table 709.1), a water closet (toilet) with a 1.6 gpf flush valve is rated at 4 DFU. A lavatory (bathroom sink) is 1 DFU, a bathtub or shower is 2 DFU, and a kitchen sink is 2 DFU. DFU values are used to size drain, waste, and vent (DWV) piping.

✓ Correct Answer: 1-1/4 inch

The IPC requires a minimum 1-1/4 inch trap for a lavatory. The trap must be the same size as or larger than the fixture drain outlet. A kitchen sink requires a minimum 1-1/2 inch trap, and a floor drain or water closet does not use a P-trap (it has an integral trap).

✓ Correct Answer: 6 feet

Per IPC Table 909.1, the maximum trap arm length for a 1-1/2 inch trap arm is 6 feet. For a 1-1/4 inch trap arm, the maximum is 5 feet. For a 2 inch trap arm, the maximum is 8 feet. Exceeding these lengths can allow siphoning of the trap seal, allowing sewer gases into the building.

✓ Correct Answer: A wet vent may serve as both a drain and a vent for a limited number of fixtures

Under IPC Section 912, a wet vent is a single pipe that serves as both the drain and the vent for bathroom fixtures in a vertical wet vent group. It eliminates the need for individual fixture vents in a bathroom group. The wet vent must be sized per Table 912.3 — typically 2 inches minimum for up to 4 DFU.

✓ Correct Answer: Outside the building or to an indirect waste receptor within 6 inches of the floor

Per the IPC, a TPR valve discharge pipe must discharge to an approved location: outside the building, to an indirect waste receptor, or to the floor. The discharge pipe must terminate within 6 inches of the floor or the floor drain flood level rim to prevent scalding injury. It must not be directly connected to the drainage system (must air-gap).

✓ Correct Answer: 40 PSI

The IPC requires a minimum static water pressure of 40 PSI at fixtures (Section 604.6). Maximum static pressure is 80 PSI — a pressure reducing valve (PRV) must be installed if supply pressure exceeds 80 PSI. Flow pressure at flush valve water closets must be a minimum of 25 PSI at the valve.

✓ Correct Answer: 1/4 inch per foot

The IPC requires horizontal drainage pipes 3 inches or smaller in diameter to slope at a minimum of 1/4 inch per foot (2%). Pipes 4 inches or larger may slope at 1/8 inch per foot (1%). Insufficient slope causes solids to settle and creates blockages; excessive slope (greater than 45 degrees) can separate liquids from solids.

✓ Correct Answer: At each change of direction greater than 45 degrees, at the base of every stack, and at intervals not exceeding 100 feet

Per IPC Section 708, cleanouts must be provided at: each change of direction greater than 45 degrees in horizontal drainage piping, the base (lowest end) of every drainage stack, and at intervals of 100 feet or less in horizontal piping. Cleanouts must also be accessible and sized to allow full-bore cleaning equipment access.

✓ Correct Answer: The downstream system poses a high-hazard contamination risk to the potable water supply

An RPZ assembly is required where a high-hazard cross-connection exists — such as connections to boilers using chemical additives, irrigation systems using reclaimed water or fertilizer injection, medical equipment, or industrial chemical processes. An Atmospheric Vacuum Breaker (AVB) is used for lower-hazard situations like hose connections. RPZs must be installed above grade, accessible, and tested annually.

✓ Correct Answer: Lead pipe for new installations

Lead pipe is prohibited for new DWV installations under the IPC and all modern plumbing codes due to toxicity. Approved DWV materials include PVC Schedule 40, ABS, cast iron, galvanized steel (for certain uses), and copper DWV. Lead was historically used for closet bends and caulked joints but is no longer permitted in new work.