Originally Posted by rbigsby
Measuring the fuel tank dimensions indicates it is about 200 gallons. The sight tube read 1/2 full at the outset; adding 40 gallons to lower port didnít move the level; adding 60 gallons to upper port filled the tank!
We also can surmise that adding 60 gallons to a 1/2 full 200 gallon tank won't fill it. So either 1) it's not 200 gallons, 2) your gauge is wrong and it was either not half full or it's not full now, 3) the tank is not regularly shaped and is tapered toward the top, 4) you got a good deal at the pump because you paid for 60 gallons but they gave you 100.
I agree with the comment to trace the lines, as painful as that may be. It's just too important with fuel to know where everything is and what fills what.