Fixtures, Fixture Fittings, and Water Heaters
Fixture layout
Fixture spacing rules protect usability, not aesthetics. A water closet must have clearance from the centerline to an adjacent wall or partition and a clear space in front of it - commonly 15 inches to the side and a 30-inch by 48-inch clear area, with lavatories subject to similar side clearance. Questions test whether you apply the centerline dimension rather than the edge dimension. Fixtures must be accessible for cleaning and repair, securely attached, and sealed at the wall/floor joint.
Connections and materials
Every fixture must drain through a trap; fixture outlets and fittings must be of approved materials, with slip joints permitted only where accessible and only in the locations the code allows. Direct connections to drainage are prohibited where an indirect waste connection is required. Floor drains need trap primers where the trap would otherwise evaporate.
Water heaters
Water heaters require a temperature-and-pressure relief valve, with a discharge pipe that is the full size of the valve outlet, gravity-drained, unobstructed, not trapped, not reduced, and not threaded or capped at the end. The pipe terminates safely - typically a few inches above the floor or to the exterior above grade. A drain pan is required where leakage would cause damage, drained indirectly to a conspicuous point. Where a check valve or backflow preventer creates a closed system, thermal expansion control is needed. Gas units need combustion air and venting; all units must be accessible and labeled.
Worked example: a heater with a plugged relief valve outlet fails immediately - the outlet must never be capped, and the discharge cannot run uphill or terminate where scalding water can contact occupants.