It's way easier than that. The AD trucks with the in-cab gas tank have a petcock on the bottom of the tank. Just close the valve, take off the hose, put a jerry can under it, and open it up and it will drain right out. That's one of the only redeeming qualities of the AD's gas tank. Or, if you are just replacing the line, just shut it off and turn it back on when you are done, no need to drain the tank.
