A breakaway gas cap is filling solution tha racers use to fill there quads, race bikes, race cars so that no fuel is spilled on unit and the gas flows into the tank with no pressure build up. The fill bottle has a vent tube so escaping gases and air is exspelled from the tank as fuel enters the tank. Soon as the tank is full you pull the fill bottle away the cap closes off without so much as drop spilled. Have you watched an Indy race they fuel their race cars with the same concept.

 

Well I guess I did know what it was having a brain cramp last night