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Plumber Red Seal · Question

What is the primary factor, besides the total drainage fixture units (DFUs), that determines the required size of a horizontal sanitary building drain?

The grade (slope) of the pipe dictates the velocity of the effluent. A steeper grade allows for a smaller pipe to carry the same hydraulic load (DFUs), while a

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Question: What is the primary factor, besides the total drainage fixture units (DFUs), that determines the required size of a horizontal sanitary building drain?

Answer options:

  • The length of the building
  • The number of cleanouts installed ✅ The grade or slope of the pipe
  • The material of the pipe

Correct answer: The grade or slope of the pipe

Explanation: The grade (slope) of the pipe dictates the velocity of the effluent. A steeper grade allows for a smaller pipe to carry the same hydraulic load (DFUs), while a shallower grade requires a larger pipe to maintain proper scouring action.

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