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Plumber Red Seal · Question

What is the maximum allowable horizontal distance between a P-trap and its protecting vent for a 1.5-inch fixture drain?

According to the NPC, the maximum trap-to-vent distance is based on pipe size to prevent self-siphonage. For a 1.5-inch pipe, this distance is 1.8 meters (6 fee

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Question: What is the maximum allowable horizontal distance between a P-trap and its protecting vent for a 1.5-inch fixture drain?

Answer options:

  • 1.2 m (4 ft) ✅ 1.8 m (6 ft)
  • 2.4 m (8 ft)
  • 3.0 m (10 ft)

Correct answer: 1.8 m (6 ft)

Explanation: According to the NPC, the maximum trap-to-vent distance is based on pipe size to prevent self-siphonage. For a 1.5-inch pipe, this distance is 1.8 meters (6 feet).

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