If that is 2 inches of pipe, it would be 146.87 gallons.And, the 2 inches would have to be the inside diameter.
If that is 4 feet tall and 18 inches in diameter, it would be 16.83 gallons.
The volume is 23,430 cubic inches which would require 101.4 gallons to fill.
the diameter would be 7 inches
If it is a round 18' in diameter and a constant 52" deep then the volume is 158.6 gallons per inch. 52 inches would then be 8247.2 gallons.
The height of 400 gallons of water would depend on the shape of the container. 400 US gallons has a volume of about 206,000 cubic inches, so if the inside of the container was about 59 inches square, it would also be about 59 inches high.
If you mean inches, the tank would hold up to 11.64 gallons of water.
If the pool were filled all the way to the top it would hold 4,551.4 gallons of water. However this is generally not recommended. If filled to within 6 inches of the top (3.5 ft) it would hold 3,976 gallons.
Filled to the top, this well would hold about 956 gallons of water.