It depends on the dimensions of the tube, but the question did not provide all of them.
31.987 gallons per foot.
The volume of water in a 4-inch diameter, 1-foot section of pipe is 0.6528 gallons of water.
A three-inch diameter pipe one foot long holds 0.367 gallon.
much water per foot will a 5 inch pipe hold
17,000 gallons
7,480.52 gallons for every inch of depth
A 12 inch diameter round pipe will hold 4.89 UK gallons or 5.88 US gallons per foot.
16 and 7/8
0.212 331 gallons per foot.
10,408 US gallons.
1 acre = 43560 sq.feet. 1 foot deep water over an acre is 43560 cubic feet, which is 325851.4 gallons in 1 foot deep. If it is 1 inch deep (1/12 foot) then it is 27154.3 gallons in 1 inch deep.
The capacity of the tubing is 94.6 Imperial gallons, or 113.6 US gallons. There need not be any water in it!