What's the question? There's all different slopes. I've seen some that are practically flat - depends on the area usually. I believe here sewer has to be a minimum of 1%. But I don't think there is a minimum with storm drain - as long as it has SOME fall. Probably depens on your area, and if youre just doing it for yourself then that's definitely all that matters I would think.
For drainage plumbers use 1/32 bend, 1/16 bend, 1/8 bend short, long sweeps and 1/4 bends Converted to IPS 11.25 - 22.50 - 45 deg 60deg and 90 deg
With a level
1/8 " - 11/2".
Only if the people want the contents to flow back or forward.
One quarter inch per foot is standard "slope". This equates to a quarter bubble on a level. If you don't have at least one eighth of an inch "slope", your drain will not work properly and will clog constantly.
Radio Shack "drain pipe tracer".
Foul Air
Yes, a sewage drain pipe can be too large.
Here we have a triangle with angle A 7.5deg and opposite side O 13m, and we're looking to find the hypotenuse H which would be the drain pipe. Remember sin A=O/H, so H=O/sinA. H=13/sin7.5= 99.6m
1 in 150 for each pipe is better
One-quarter inch per foot is both the standard practice all around the country and the minimum slope (or grade) allowed by most codes. If maintaining that much slope is a problem, an exception can be requested from the administrative authority.
If you are talking about a roof water drain pipe to sewer it is illegal. If you are talking about a sink drain pipe well that is where they all connect to so yea.
dvw pipe = drain, waste and vent pipe.