If your car breaks down with a full tank of gas or one of your vehicles is empty and the other is full, you may want to siphon the gas out of your gas tank. This process is simple and, when done right, does not result in gas getting in your mouth. Remember, however, that siphoning gas out of someone else's car is illegal; do not use this method to steal gas.
Place a 5-allon bucket on the ground to catch the gas when it starts to flow out. Cut a length of clear plastic hose, with a diameter small enough to fit into your gas tank, to a length of 6 to 8 feet. Do not use a garden hose. You will not be able to see the gas flowing into the hose unless the hose is clear.
Check that your car is turned off, and unscrew the cap from the gas tank. Insert one end of the hose into the gas tank, and push it down below the gas line. If you're unsure whether it's below the gas line, blow into the hose and listen for a bubbling sound. If you don't hear one, push the hose in further.
Lower the other end of the hose so that it touches the ground, then wrap it around in a circular motion to create a loop. Stand on a sturdy chair or a box so that you can hold up the end of the hose higher than the gas tank of the car.
Clean the hose to sterilise it, and slowly suck on the end. Watch for the gas to start flowing into the loop. As long as you're holding the end of the hose well above the gas tank, the gas shouldn't come up through the loop and into your mouth. This eliminates the risk of swallowing gas; however, you should still go slow for your safety. Once you see the gas filling up the loop, stop sucking on it.
Place the hose into the bucket, and move the hose around so that the loop straightens out and the gas begins to flow into the bucket. It should all flow out into the bucket, and you can then remove the hose and replace the gas cap. If the gas stops flowing for some reason and you think more gas is still in the tank, do not try to get it out. You'll need to thoroughly wash and sterilise the hose before attempting the process again.
Consider purchasing a small pump and hose from an automotive store if you don't want to suck on the hose yourself.
Newer cars have security devices to prevent gas theft. If you cannot get the gas out of the tank, it may have a security feature that prevents siphoning of gas out of your car.