I forgot to add in the rectangular part. The part left over is a rectangle that is 5 x 27 x 60.
Add the volumes of the cylinder part to the rectangular part to get the total cubic inches.
However, my formula is based on the top and bottom halfs but together will make a cylinder. It's possible the top curved part will look more like half a foot ball, oval shaped, in which case without exact measurements, the exact answer will be a guessing game.
Based on a cylinder and rectangle, my answer is 184.3 gallons. If it's oval shaped top and bottom, then the volume will be more.