I'd like to understand more about how this system works. Specifically, I read of a person that stole huge amounts of fuel by parking a modified van over (I don't know which port), popping up a hatch cut in the rear of the van floor, and pumping fuel into tanks inside the van. When I've looked at the ports where tankers fill up (with permission) they don't appear to have a direct route into the tank where the thieves could drop in a pump.

How would that type of attack work?