We all use the term “DFU” (drainage fixture unit) when referring to a load value assigned to a particular piece of pipe, but where did the DFU come from?
Dr. Roy B. Hunter coined the term DFU. Instead of plumbers trying to figure out exactly how full each pipe is, Hunter based the DFU on the smallest load value of a fixture, which was the lavatory. The lavatory with a concave bowl shape entering the drain discharged at a value of about 7.5 gallons per minute. That amount is really close to a cubic foot of water, so he coined that
