Here are some ideas.
Try logging onto a Balzer forum and ask if anyone knows.
Call a dealership and ask.
This might not be practical, but it will work. Weigh the tank while it's empty.
Fill it with water WHILE it is still on the scale. Calculate the weight of the water and then divide by how much a gallon weighs. I hope that doesn't sound silly. It should work. Or pour out the water into a measuring device.
Calcualtion with length, width, height will be less accurate but might be close enough for your purposes.
I wanna see what others say.
