Ken;
I can't say for certain but I would assume when working with a tank that size you would not be dealing in cubic inches, but cubic feet or even cubic yards. the formula works identically for any unit of measurement as long as you keep all components on the same scale. Thus if you use feet for the diameter you have to also use feet for the length/height of the tank.
As to Pi xDČ/4 versus Pi x RČ they are of course the exact same formula. As R = D/2 then (D/2)Č DČ/4. When I am using this area formula I will normally be working with a diameter rather than a radius so I just Sq the D & divide by 4 rather than divide D by 2 & sq the result. Multiply by Pi either way. Exact same number of keystrokes on my faithful Casio Calculator.
I have absolutely not the Foggiest idea where that &#960 came from. I held down the alternate key & typed 227 & the Pi symbol came up. When I post every time it has thrown in that &#960 instead. I have gone back & edited & used the letters Pi instead of the symbol. The listing I have for these says to hold Alt & the Windows symbol but for ages I have only held the alt key & it has always worked. As a test I am going to try Alt & Win then 227 & see if it transports OK.
Test = π
Obviously that's not the problem, When I typed it in it came up with the Pi symbol plain as Day but when I send it comes out this GobbledeeGobble.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra