[Ghostmaker]

There is no max pitch in the IPC code. It also is a myth that once you flush a toilet the water carries it out of the house. It takes multiple flushes And most of the time what leaves is a slurry. Apply what you know.

 

[Ghostmaker]

This is for a ~100 horizontal run from a pool house w toilet and sink to to the home main line. I don’t want it to steep for the run or the liquids will out run the solids.
I will have a 2’ vertical drop to the drain line into the horizontal run.

There is no max pitch in the IPC code. It also is a myth that once you flush a toilet the water carries it out of the house. It takes multiple flushes And most of the time what leaves is a slurry. Apply what you know.

You also need 12.5 inch fall for that 100 foot run at 1/8 inch per foot.

 

[Ghostmaker]

Apparently, at least some local codes (NYC for one) have a max slope for sewer lines where they enter the mains, but it's 1/4, in order to avoid disruptions, scouring, backflow into other lines, etc. due to high velocity flows.

I don't know that I'd dismiss the 'liquids running away and leaving the solids' concept as a "myth", but at the least, it's apparently not a big enough or common enough issue to be addressed in the code. Of course, all new sewer installations are smooth wall pipe, which was not always the case, so it may be an issue that was resolved by the changes in type of sewer pipes in use.

That said, if I was laying a sewer line, I would keep to 1/2" per ft or less, and then 45 degrees drops, if I could.

I just base it on observations of what happens with a river. When a river is flowing fast it moves rocks. When a river slows and spreads it drops all it carries.

 

[Ghostmaker]

I suppose if you leave all of your faucets running all of the time that might work.

The only sewers I have seen clog were either flat with no pitch or ones with bows in the plastic. But in my lifetime as a plumber I have never seen a sewer with high pitch clog.