u/burntoutpotato

Okay, I have 2 theories. To maintain pressure and ensure the sewage flows away from origin, either

1. A system pressurize the sludge is utilized.

2. A downward gradient from origin to out is maintained.

3. seems unlikely to me having not seen any pressurizing unit at most places.

In that case, if 2) is true, how does one get a contant downward gradient for the severs when the geography around has so many extreme ups and downs? Even a 1 degree downward slope over many miles would be hard to achieve.