Now the question. I understand that the min.drop for 3 in. drain is 1/8 per foot. Some of my browsing has lead to drop calcs of 7 feet or so over 60 feet. My drain farthest from the old sewer pipe is around 40 feet so at .125 x 40 is 5 inches, right? 1 inch drop for every eight feet.
If your run is 60 feet, your total drop or fall with be 60 feet X 1/8" per foot or
60/8ths vertical drop.
60/8ths converts to 7 1/2 inches
total drop over 60 feet.
For a 40 foot run, your total drop or fall will be 40 feet X 1/8" per foot or 40/8ths vertical drop.
40/8ths = 5".