A plumber is installing a 76 mm diameter building drain. The code specifies a minimum slope for this size of pipe to ensure adequate self-cleansing velocity. According to the National Plumbing Code of Canada (NPC), what is the minimum required slope for a 76 mm building drain?

Question: A plumber is installing a 76 mm diameter building drain. The code specifies a minimum slope for this size of pipe to ensure adequate self-cleansing velocity. According to the National Plumbing Code of Canada (NPC), what is the minimum required slope for a 76 mm building drain?

Answer options:

• 1 in 50 (2%) ✅ 1 in 75 (1.33%)
• 1 in 100 (1%)
• 1 in 150 (0.67%)

Correct answer: 1 in 75 (1.33%)

Explanation: According to NPC Table 2.4.6.2. (or similar provincial tables for drainage pipe slopes), the minimum slope for a 76 mm (3 inch) building drain or branch drain is 1 in 75. This slope ensures adequate flow velocity to prevent solids from settling and causing blockages.