text: i need to find out how fast water will drain from a 2" pipe for a tank overflow?   how long is the length of the pipe, and is there any siphon effect? what is the difference in elevation?  uniform plumbing code 2000 requires a 2" drain for 16-30 gallons/minute worth of "fixture units" it would require minimum 1/8th inch/ft of slope.  the actual calculation is quite complex.