Here'* a math problem for people that like math. Say you have a pipe that is 12 points 9 inches inside diameter... 3000 feet of it is filled with liquid and needs to be drained through two 3/4 quarter inch lines. what is the total volume of liquid that will be drained and how long will it take using only gravity.

20,367 gallons
7.462 hours

(12.9/2/12)**2 x 3.14159 x 3000 = 2722.9 cubic feet
x 7.48 gallons per cubic foot = 20,367 gallons

The time is just a number I made up. It can't be calculated since you don't know the slope of the pipe. If it is sitting perfectly flat it will never completely drain. If you stand it straight up it will drain in 2 minutes.

And by the way, you need an engineer, not a mathematician.

Your saying a 3000ft pipe standing straight up filled with water will drain in 2 minutes out of (2ea) 3/4" holes?

I'm saying you need to know the slope of the pipe to know how long it will take to drain.

I wasn't exactly given that info, but lets say for practical purposes, the pipe is vertical and the 2 holes are equal distant at the bottom.