We are installing a 120 foot run of sewer line down a hill and aross a creek into the city sewer system. The city have provided a connection and we have installed a cast iron pipe on top of concrete pillars to go across the creek into the city connection with a 1/4" per foot slope into the sewer.

The land slopes away from the house at a reasonable slope and then dips down again towards the creek. Is it permissible to go steeper (say 45 degrees for a while) to keep the pipe underground and how deep does the 4 inch pipe need to be under the ground please?

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Originally Posted by pughimag

We are installing a 120 foot run of sewer line down a hill and aross a creek into the city sewer system. The city have provided a connection and we have installed a cast iron pipe on top of concrete pillars to go across the creek into the city connection with a 1/4" per foot slope into the sewer.

The land slopes away from the house at a reasonable slope and then dips down again towards the creek. Is it permissible to go steeper (say 45 degrees for a while) to keep the pipe underground and how deep does the 4 inch pipe need to be under the ground please?

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How deep your pipe will start at will be dictated by the degree of slope on the hill. On a 120 foot run you will have 2 1/2' (30") of fall at 1/4" slope to the foot. So you would start at the street raiser and figure backwards to see how far down to 45 until you began the run to the street. If you're in a warm climate, like we are here, you can start outa few feet under the ground and slope to the raiser and 45 down to connect after you reach it.
Good luck, Tom