What is the minimum slope for 6 inch underground sewer pipe?

1/4" per ft. is the lowest allowed.

1. Allowed by whom? Not many regulatory authorities specify the minimum slope of a 6" sewer pipe.

2. Why state in inches, typically engineers use a 2.0% or 0.02 / 100' form for the answer.

3. Using Manning's of 0.013 (although most PVC could use a 0.009 or 0.011 n factor, you can achieve the 2 ft/sec typical requirement with a slope of 0.005 or 0.5%, although it was stated to me that 0.0067 or 0.67% is the correct minimun slope to use. I am just trying to find that source which is tough as most authorities do not specify the minimum slope of a 6" pipe.