A continuous-flow drainage device discharges 5 GPM. How many drainage fixture units (DFU) should be assigned?

• A. 5 DFU
• B. 15 DFU
• C. 20 DFU
• D. 10 DFU

Answer: (D)

DFU, or drainage fixture unit, is a sizing measure used to estimate the load a drainage system must carry. For continuous-flow drainage devices, the DFU value comes from a table that converts gallons per minute into DFU. In this context, the standard approach doubles the flow to get DFU, so 5 GPM corresponds to 10 DFU. This reflects how the code accounts for the typical impact of continuous discharge on the drainage network. If you were combining multiple fixtures, you’d sum their DFU values to size the piping. The other numerical options don’t align with this conversion for continuous-flow devices, which is why 10 DFU is the correct assignment.