Fixtures, Fixture Fittings, and Plumbing Appliances
Fixture Requirements
Each fixture must be listed and labeled, have a smooth and cleanable surface, be properly supported, and be trapped and vented. Know the water-saving thresholds: water closets at 1.28 gallons per flush and urinals at 0.5 gallons per flush are the modern baselines, and questions often test whether a replacement fixture may exceed them (it may not). Lavatories commonly take a 1-1/4 inch drain, water closets a 3 inch drain, and a clothes washer requires a standpipe and trap in the trap-arm sizing tables.
Spacing and Installation Traps
- Water closet clearances: about 15 inches from the centerline to a side wall and about 21 inches of clear space in front.
- Trap seals must be 2 to 4 inches deep; an unvented or shallow-sealed trap invites sewer gas.
- Floor drains in areas that dry out need trap primers; a dry trap is a code violation and a health issue.
- Dishwashers need an air gap or an approved high-loop drain arrangement, never a direct connection below the flood level rim.
- Water heaters need a temperature and pressure relief valve, a drain pan where leakage causes damage, and correct clearance from combustibles.
Worked Example
Replacing 1.6 gallon-per-flush water closets with 1.28 gallon models: a family of four flushing five times daily saves 20 x 0.32 = 6.4 gallons per day, about 2,336 gallons per year. Use that arithmetic in questions comparing fixture options, and remember that local water-conservation rules can be stricter than the plumbing code.