I don't know about UPC and specifically 6" sewers, but in our area I believe most mainline sewers are limited to 8" minimum size. However, I believe ASCE MOP No. 60 (WPCF MOP No. FD-5), "Gravity Sanitary Sewer Design and Construction" (talking I think mostly about smaller service lines), contains the quote, "It is common to lay house connections at a slope of 2%, with a minimum slope of 1%."
In PA, USA, 6" is allowed to go to 0.006, per PaDEP.
Also, in PA, generally a publicly owned main is not allowed to be under 8". But laterals usually are. Those are laid at a min of 1%, 2% is desired for scour.
Engineering is the practice of the art of science - Steve
