One of my favorite stunts...

The KC/EC-135's use water injection for takeoff. If you hang a new engine on an airplane you have to trim it or if there was an issue with the water injection pumps/generators we'd have to do an engine run which included an ops check on the water system. So you get a rookie to act as ground man for the engine run. We hardly ever run all the water out during the run so the tank has to be drained. There's a drain mast sticking out of the belly just aft of the landing gear doors. After you shut down the engine/s you tell the rookie there's a light inside the drain mast that must be checked after each run. Problem is he has to get real close, cup his hands over the mast and look inside. The light is hard to see. Once he's in place I'd reach over and flip the switch... which dumps the water. Oops! grin