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Changing from a residential single unit dwelling, septic tank to county sewage system.
What is the minimum slope/fall for a 4" lateral pipe that is 119 feet in length for a residence to a sewage tap.
Around these parts......29.75 inches. 1/4" per lineal foot is the desired slope.
But the inspector will allow some variance depending upon the situation.
(They'd sooner see steeper than flatter.)
For North Carolina it it 1/8 slope for 4" pipe with a bed of gravel underneath. Depending on the inspector, they might require it to be atleast 6" underneath (i usally try for 3" to allow for grade changes).
Something you didn't mention is the path of the run. It is 120' but are there any turns? You will need a cleanout for any turn over 135 degrees. And it never hurts to have one at the top of the run and the bottom of the run for a mainline run if needed. Right outside your house should be a double cleabnout or a "Cinncinati Cleanout" and then you have the one at the county main (2 minimum. Good luck. Process of Elimination.