In 1 foot of 10in diameter pipe there are pi x 52 x 12 cubic inches (where pi = 3.1416) which is 942.48 cu ins. I US gallon = 231 cu ins 1 Imperial Gallon = 277.4 cu ins. So 942.48 cu ins is 4.08 US gallons or 3.4 Imperial (UK) gallons It makes no difference what the pipe is made from or what the liquid is.
2.6112 gallons per foot
31.987 gallons per foot.
Each foot of a 4-inch diameter pipe has a water volume of: 0.652 gallons.
There can be no "per foot" measure for a spherical container. A 6 inch diameter ball will hold 0.49 US gallons.
106.12 US gallons per foot of 51-inch-diameter pipe.
14.688 US liquid gallons
The volume of water in a 4-inch diameter, 1-foot section of pipe is 0.6528 gallons of water.
A 12 inch diameter round pipe will hold 4.89 UK gallons or 5.88 US gallons per foot.
2.6 gallons of water.
I assume you mean 5 foot diameter AND 6 inches deep: 9.8125 cu.ft. = 73.3975 gallons
A 24-inch diameter cylinder holds 23.5 gallons of water per foot of length/height.
Over 9,000.