This story wasn't my granddads but he was old enough to be mine. Anyway, he had a motor home and some kids were stealing gas out of it and were getting a bunch. It happened 3 times and he decided to do something about it. One day he brought it to my house with enough hose to switch the gas hose to the black water holding tank. After he was done, he took it home and parked it. Next morning lo and behold, there were 3 gas cans, a rubber 5/8 tube sticking out of the now modified gas fill up and a bunch of puke all around. He never lost another drop of gas.