An air gap in a drainage system is the unobstructed vertical distance of free space between the outlet of the waste pipe and the flood-level rim of the receptacle into which the waste pipe is discharging. As an example in a commercial restaurant, the air gap would be between the drainpipe of a salad bar and the floor sink or tub drain.

A water heater tank should be installed inside a pan in locations in a dwelling where a leak from the tank could cause damage to the structure or property. The pan is intended to catch water leaks from the tank or associated connections, or condensate from the tank. The pan should be made of galvanized steel or other material approved for that use. Pre-fabricated aluminum and plastic pans are common and widely used. Aluminum and plastic pans may not be allowed by every authority having jurisdiction (AHJ) or code official because they are not made of galvanized steel, and some tank manufacturers require the use of a metal pan only.

The following are 13 requirements for a discharge pipe serving a TPR valve:

Temperature and pressure-relief (TPR) valves are safety devices installed on water heating appliances, such as boilers and domestic water supply heaters. TPRs are designed to automatically release water in the event that pressure or temperature in the water tank exceeds safe levels.

If a laundry tub waste line connects to a clothes washer standpipe, the standpipe should be at least 30 inches above the standpipe trap weir and should extend above the flood level rim edge of the laundry tub. The outlet of the laundry tub must not be more than 30 inches horizontally away from the standpipe trap.

Whirlpool/jetted bathtub fixtures must be installed according to the manufacturer’s recommendations. The bathtub may be filled with water and tested during the rough-in plumbing inspection.