That raises an interesting question. On the Earth I do believe that there is a standard minimum slope for plumbing to follow.
Oh boy. That does open up another huge can of worms. Who would have thought that plumbing could get so complicated? The minimum slope depends upon pipe size. There can be a maximum slope too since one does not want the stuff going downhill to be moving too fast when it hits the sewer mains. And another thing to consider, the lines would have to be under pressure and heated since the "p traps" do not work if they dry up. They need water in them to work to block sewage gases:
Pitch on a sewer line or drain pipe is also called slope. Many are unsure of what proper pitch is for a house drain pipe, but there is a formula.
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