A plumber is roughing in the drainage for a commercial kitchen. The drainage system will include a floor drain with a 75 mm nominal pipe size and a grease interceptor. When calculating the total drainage fixture unit (DFU) load for this section, what DFU value should generally be assigned to a 75 mm floor drain with a grease interceptor as per the National Plumbing Code of Canada?

Question: A plumber is roughing in the drainage for a commercial kitchen. The drainage system will include a floor drain with a 75 mm nominal pipe size and a grease interceptor. When calculating the total drainage fixture unit (DFU) load for this section, what DFU value should generally be assigned to a 75 mm floor drain with a grease interceptor as per the National Plumbing Code of Canada?

Answer options:

• 2 DFU
• 3 DFU
• 4 DFU ✅ 5 DFU

Correct answer: 5 DFU

Explanation: According to NPC Table 2.4.9.4.(1) (or similar provincial tables), a floor drain (commercial/industrial, 75 mm) connected to a grease interceptor is assigned a drainage fixture unit value of 5 DFU. This value accounts for the potential heavy waste flow and the additional resistance from the interceptor.