Sewer Line Slope

Yep. One-quarter inch per foot (approximately).

Good morning Guest.

So, for in the US, in the earth under the floor of a single story building, carrying the waste of 3 WC's, a urinal, and 4 lavs, in DFU's of 6, 6, 6, 2, 1, 1, 1, 1, or a total of 24 DFU's, you'd specify a 4" size, because a 3" can only support 20 DFU's, per the IMC P62, correct?

And this pipe would be 4" SDR 35 (0.120"wt), 4.215" OD PVC, at 2% slope, or 1/4" / ft, and not 4" Sch 40, 4.5" OD PVC, correct?

It seems a little surprising the industry did not just specify the Sch 40 for the extra strength it would provide, but I guess the cost differential was enough to justify this thin-wall, special OD pipe and fittings.

The numbers I've typically seen for required drain slope are :

a minimum 1/4" per foot (2%) slope for 3" diameter or smaller
a minimum 1/8" per foot (1%) slope if larger than 3" diameter

however, please verify the correct numbers with your local plumbing inspector. He should be familiar with your local code requirements and will be the one who passes or fails your installation! Local and regional codes usually start with the larger UPC/IPC standards, but many supersede them with stricter requirements.

you are correct! Figures don't lie only liers figure