That's funny, it took me a second to realize that a regular hex tank would be six equilateral triangles of side length "s". I as just about to get into the sqrt(3) part and then reduce it from there, when I figured someone must have gotten there already. Good show, Matt.
I have a flatback Hex, and the way I get the volume of that one is to calculate it as if it were a rectangle, then subtract the volume of the square prism you get by considering the beveled sides together.
