A. DFU stands for Drainage Fixture Unit. Each plumbing fixture or appliance is assigned a particular drainage fixture unit value as determined by the International Association of Plumbing and Mechanical Officials
(IAPMO). For example a kitchen sink is assigned 2 fixture units, but a bathroom sink is assigned 1 fixture unit. Drainage fixture units are used by plumbers and engineers to determine the size of piping needed for proper drainage and vent
systems. A listing of plumbing fixtures and appliances and their fixture unit values can be found in Chapter 7 of the Uniform Plumbing Code (UPC) book.