For a 2" drain pipe horizontal run in a bathroom, what is the correct slope drop per 10 feet?
Also, can a single 2" drain pipe support a separate tub, shower and 2 sinks?
Plumbing – what is the correct slope for a 2″ horizontal drain pipe
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Related Solutions
From the 2012 International Plumbing Code Section 1106, I get a pipe diameter of 3" based on table 1106.3 and this map:
Comparing the pressure drop between 50' of 3/4" and 1" PEX...going up to 1" saves 1 psi at 5 GPM flow rate, and 5 psi at 9 GPM and 7 psi at 11 GPM (when you hit 10 feet per second in 3/4" PEX, a velocity which shouldn't be exceeded). In other words, you need to have pretty significant concurrent demands before the pressure drop in that pipe run becomes noticeable (or where pipe erosion from high velocity becomes a concern) - like filling two tubs or taking four showers at the exact same time, plus running a dishwasher or washing machine. It's possible that with so many kids that's actually a reasonable concern for you, but for the typical household there would be little benefit.
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Best Answer
1/4 inch per foot is most common and is the minimum allowed. Maximum allowed is 3 inches per foot
So on a 10 foot section that would be 2.5 inches total slope minimum and 30 inches maximum.
For the second part of your question see the answer to this question.