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Finding the Required Slope of a Sewage Pipe

Sewage pipes running from a house to the street must slope downward at a rate of 14\frac{1}{4} inch per foot in order to drain properly. To find the required slope, apply the rise-over-run formula, making sure both measurements use the same unit.

Write the slope formula and substitute:

m=riserun=14 inch1 footm = \frac{\text{rise}}{\text{run}} = \frac{-\frac{1}{4} \text{ inch}}{1 \text{ foot}}

Convert the run to inches so the units match (11 foot =12= 12 inches):

m=14 inch12 inchesm = \frac{-\frac{1}{4} \text{ inch}}{12 \text{ inches}}

Simplify by dividing 14-\frac{1}{4} by 1212:

m=148m = -\frac{1}{48}

The required slope of the pipe is 148-\frac{1}{48}. This means the pipe drops 11 inch for every 4848 inches of horizontal run. The slope is negative because the pipe must angle downward to allow gravity to move the sewage toward the street.

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Updated 2026-04-21

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