Siphons are an arrangement of tubes used to move a liquid from a higher source to a lower container by taking advantage of gravity and a difference in atmospheric pressure. The movement of the liquid can be initialized by applying external suction or by pre-filling the tube with liquid, and then allowing the weight of the liquid at the source to push the liquid through the tube. When using a gas siphon it is usually not feasible to pre-fill the tube, so some type of suction must be applied to initiate the movement of gasoline.
Remove the gas fill cap from the vehicle. Insert the long end of the siphon hose into the gas fill spout and push the hose into the gas tank as far as possible, or until the rubber ball on the hose contacts the opening.
Place the gas can on the ground and remove the cap. Insert the short end of the siphon hose into the gas can. Be sure there are no kinks or loops in the lower end of the hose as they will impede the siphoning action.
Squeeze the rubber ball with your hand until the gasoline starts to flow through the hose. Stop squeezing the ball once the gasoline begins flowing steadily. Allow the siphoning action to fill the gas can. If the flow of gasoline stops the end of the hose may be resting against an obstruction, such as the side of the gas tank. Pull the hose out of the tank a few inches and squeeze the bulb until the flow of gasoline resumes.
