What is the minimum slope required for the horizontal drainage piping sizes typically covered by the UPC's sizing tables?
Not quite. The answer is A: 1/4 inch per foot
Horizontal drainage piping must be run at a uniform slope of at least 1/4 inch per foot (2 percent). Only where that is impractical because of the depth of the street sewer or structural features may pipe 4 inches and larger be laid at 1/8 inch per foot, and then only with the authority having jurisdiction's approval. Enough slope keeps solids moving with the liquid instead of leaving them stranded.
Reference: UPC 2021 §708.1 (Grade of horizontal drainage piping)
Checked against the official text
Checked against the 2021 UPC text. Washington's exam is written against the 2015 edition, which we have not read for this section, so confirm it against your 2015 book.
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