Fixtures, Faucets, and Fixture Fittings
Fixtures, Faucets, and Fixture Fittings covers the appliance side of plumbing: fixture selection, trap size, flow rates, backflow protection, and the connections that join fixtures to the drainage and water systems. The exam tests whether a fixture can be installed as shown and whether its trap and drain are legal.
Core rules
- Minimum trap sizes commonly include 1-1/4 inch for lavatories, 1-1/2 inch for kitchen sinks and bathtubs, 2 inches for showers and floor drains, and 3 inches for water closets.
- A trap may not be reduced in size downstream in the direction of flow.
- Dishwashers need an air gap or approved backflow device; hose bibbs need vacuum breakers.
- Fixture openings must be accessible for cleaning, and slip joints must be accessible unless approved.
- Water closets, urinals, and similar fixtures have specific flush-volume and connection requirements in the adopted code.
Worked example
A lavatory has a 1-1/4-inch trap outlet connected to a 1-1/2-inch branch drain. Is that acceptable? Yes. The trap is the minimum size for the lavatory, and the drain increases downstream; no reduction occurs in the direction of flow. If the same lavatory had a 1-1/2-inch trap connected to a 1-1/4-inch drain, it would be a violation because the pipe reduces downstream.
Traps that cost marks
- Upsizing a trap without checking the fixture drain size.
- Omitting the dishwasher air gap or vacuum breaker.
- Installing a fixture with an inaccessible cleanout or slip joint.
- Confusing maximum fixture flow rates with trap sizes.