375.7952 gallons per foot of 96" pipe
One square foot
4in diameter pipe 1 foot long L*pi*r2 = volume, where L=12 in and r=2 in 12*3.14*22 = 150.72 in3 1 in3 = 0.004329 gal , therefore: 150.72 * 0.004329 = 0.6525 gallons
Depends on many factors, such as smoothness of pipe, hydrostatic head, etc. But you can expect anywhere from 50 gal/min to 150 gal/min.
3400 gal
1 cubic foot is 6.2 (6.22883) Imperial gallons.
5000 gal
1/2 inch will easily do that.
Fill up a 5 gal bucket of water at full pressure and time it.
Assuming the 6 inches refers to the inner diameter so that the radius is 3 inches, the capacity of the pipe is pi*r2*l = pi*32*12 = 339 cubic inches approx = 1.47 US gallons. There is, of course, no way of knowing how much water there is in the pipe except that it cannot be more than 1.47 US gal.
213,000 gal / 7.48 gal /cubic foot =28,476cf /12ft(depth)=2373 sqft of surface area
Assuming that the INNER DIAMETER of the PVC pipe is 4" (...likely not the case, so you'll need to recalculate for your pipe's dimensions): the volume of the pipe would be calculated as follows: 4" diameter = 2" radius volume_cylinder = Pi*r^2*L; where r = 2" and L = 12" the cylinder therefore has a capacity of 150.8 cubic inches. a gallon of water has the volume of 231 cubic inches. your pipe can hold 0.653 gallons of water. you'll need about 18.38 inch lengths of 4" PVC to hold each gallon of water. again, these calculations rely on the INNER DIAMETER of the pipe being measured at 4" - if this is an outer diameter measurement, the above calculation for the capacity is OVERstated; the 18.38" calculation is UNDERstated.