How to Bypass a Gas Tank Anti-Siphon Valve

After a natural disaster, you need gas for your generator. You know the gas tank in your vehicle is full. How do you bypass the anti-siphon device in the filler tube? There is a way to get around the anti-siphon valve, but it can be tricky and will not work on some vehicles.

Fuel system technology and safety devices have made gas tanks nearly impervious to tampering. We will look at two ways to bypass the anti-siphon device installed in a modern car and then some other viable options if the traditional siphoning methods don’t work.

What Is the Anti-Siphon Valve?

The fuel fill tube of most vehicles produced today includes a rollover valve, also known as an anti-siphon valve. Anti-siphon valves prevent back-flow, relieve tank pressure, and block the gas from spilling out of the gas tank in the event of a rollover.

A plastic ball is retained by a set of clips at the end of the filler tube. Since the ball is always in place just below the filler tube’s end, it can also prevent gas siphoning.

The Safest Way to Bypass the Anti-Siphon Valve

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You should be able to slip a small plastic tube through the valve if you have the right tools. To attempt this method, you will need the following items.

Required Components:

  • 4 feet of 3/8 inch ID Polyethylene tubing
  • 6 feet of .170 inch ID x 1/4 inch OD Polyethylene Tubing
  • A sharp knife or tubing cutter
  • Gas safe pump

Polyethylene tubing is used for a siphon hose instead of vinyl tubes. The poly is flexible but relatively stiff. Vinyl is too soft for this project.

Use a 12-volt electric or manually operated fuel safe pump. Use the 0.170-inch tube as the siphon tube. It will take hours to transfer fuel with the small tube by gravity. Also, you do not want to suck gas into your mouth if you can avoid it.

The Procedure for Bypassing Car’s Anti-Siphon Valves

Disclaimer: these are general guidelines! What you do to your own vehicle is your own responsibility. We are merely sharing one way to do this to a vehicle you legally own.

Install the Guide Tube

Slide the 3/8 inch tube down the filler tube. The tube should be stiff enough to push the upper seal open. If not, use a long, thin screwdriver to push the seal open. Slide the tube down as far as it will go. You may need to rotate the tube to reach the end of the filler tube.

Install the Siphon Tube

Cut the lead end of the siphon tube at a 45-degree angle. The pointed end will assist in slipping past the valve. Slide the siphon tube down inside the guide tube.

When the siphon tube reaches the ball, pull the guide tube back an inch or two. Continue pushing and rotating the siphon tube until it slips past the ball.

Testing for Fuel

Blow through the siphon tube if you suspect it has slipped past the ball. You will hear bubbling and feel resistance if the tube has reached the fuel tank. When you reach the fuel, slide a foot of tubing into the tank.

How To Siphon Gas

You can now attach the pump to the siphon tube and draw gas out of the tank. Place the discharge end of the pump in a gas can before starting the pump.

Pull the siphon and support tubes from the tank when finished. Removal may require some back and forth movement as the ball may pinch the tube.

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Another Way to Bypass Anti-Siphon Valves

This method is similar to the first procedure. The main drawback is that it is destructive and may result in a damaged filler tube. Avoid this method unless absolutely necessary. If you are in severe need of gas, it is a viable option.

Required components:

  • 2 feet of 1/2 inch flexible copper or aluminum tubing. Do not use steel.
  • If your car’s filler tube is straight enough, 1/2 inch PVC pipe will work
  • Regular siphoning kit
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The Procedure

Insert the metal tube into the gas filler tube. Do not use steel due to the chance of making a spark. Work the tube down the filler tube until you reach the anti-siphon valve.

Pushing the tube should dislodge the ball or break the retainer clips that hold it. If you can not push the ball loose, strike the end of the tube with a hammer, as this may dislodge the ball.

Siphon Gas

If you dislodge the ball, remove the metal tube. You can now insert your regular siphon tube and remove the fuel. Use a 12-volt or hand pump to draw out the gas.

If you use a gravity system, use a bulb to draw the fuel out of the tank to start the gas flowing.

Other Ways of Siphoning Fuel From Your Car

Sometimes the traditional siphoning methods won’t work, so here are a few additional options.

Siphoning a Car’s Fuel Pump

Many modern passenger cars have fuel pump access panels in the trunk or under the back seat. Removing the electric fuel pump is an easy way to siphon the gas from your vehicle. Some cars, and most pickup trucks, do not have easy access to the fuel pump. Even if you need to work under the vehicle to remove the pump, it may be a better option than breaking your anti-siphon valve.

If your vehicle does have a fuel pump access panel, the process is straightforward.

  • Disconnect the negative battery terminal
  • Remove the access panel
  • Make a note or take a picture of the connections before proceeding.
  • Disconnect electrical connections and fuel lines
  • Remove the fuel pump

You now have clear access to the fuel tank. After siphoning the gas, replace the pump. It may be wise not to reconnect everything if you suspect you will need more gas before you need the car.

Extreme Situations

Siphoning may not be viable on your vehicle. A good mechanic could add a valve to some other portion of the fuel system. A valve installed in the fuel line or the tank itself may be an option. Such additions are not recommended but are a potential solution.

Does siphoning gas hurt your car?

There is no evidence that siphoning gas will hurt your car. The act of removing gas from the tank may cause sediment to be stirred up. This could lead to clogging of the fuel filter or other parts of the fuel system. If you are siphoning gas from a dirty tank, take care to clean the siphon tube and container when finished.

Can you use a garden hose as a siphoning tube?

A garden hose is not a good option for siphoning gas. A garden hose is not rigid and will kink. This will impede the flow of gas and could cause the hose to burst. A garden hose is also more likely to create a spark, which could ignite the fuel vapors in the tank.

Is an anti-siphon screen the same thing as an anti-siphon valve?

An anti-siphon screen is a mesh that is placed over the fuel filler neck. This screen is designed to prevent debris from entering the tank and clogging the fuel filter. It does not serve the same purpose as an anti-siphon valve, which is designed to keep fuel from being siphoned out of the tank.


“Nothing is as easy as it should be” is a phrase that comes to mind when trying to siphon fuel from your car’s gas tank. While there are methods to do it, success is contingent on the design of the fuel filler tube and the anti-siphon device. If you suspect you may need to attempt siphoning gas from your vehicle someday, it would be wise to test the preferred method before that day comes. Practice is often part of being prepared.

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