@Randy Dandy,
Well, the value 8.345 is not the amount of water in tank but instead the weight in pounds of 1 gallon of water.
So, you know that 1 ton (US) is 2000 pounds.
To know how many gallons you can put on a 2000 pounds truck, you just have to divide it by 8.345 (some say 8.33).
Gs=2000/8.345 = 240 gallons.
However, you need to take into account the weight of the tank, which is 67 pounds.
What are the equivalent gallons of that value?
TW= 67/8.345 = 8 gallons.
Then you subtract 8 gallons from your initial 240 to compensate for the tank weight:
240-8 = 232.
You can put 232 gallons in your tank on a truck that holds 1 ton.