How to Siphon Gas (Plus 6 Ways to Bypass the Anti-Siphon Valve)


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Last Updated: October 4, 2021

While I definitely don’t recommend it, siphoning gas is a good skill to know for emergencies.  You could use the siphoned gas to fuel a generator or to refuel your vehicle during evacuation.

However, it is really difficult to siphon gas from modern cars because they have anti-siphon valves and devices in them.

It’s not impossible though. You just need special tools, know-how and a lot of ingenuity.

How to Siphon Gas

1. Open the fuel door

This is the easiest part.  Even if you don’t know how to pick a lock, it’s pretty easy to open the fuel door with brute force. You can use a crowbar or the claw on the back of a hammer.

2. Use screwdriver to push aside flap over filler pipe

Almost all fuel pipes have a little metal flap over them.  The flap allows you to insert a hose in but will jam when you try to remove the siphon hose. To bypass this, all you need is a long, skinny object like a screwdriver.  Use the screwdriver to push the flap aside and hold it open.

3. Siphon the gas

Stick the siphon hose into the tank and the other end into a fuel canister.  Remember that siphons are one-way devices so make sure you put the right side of the hose into the tank. Squeeze the valve and it will suction the gas out of the tank and into your canister.

*Don’t use the old method of siphoning gas with your mouth!  The risk of getting a mouthful of gasoline is simply too great.  A squeeze-bulb type siphon will make the job a lot easier.

But wait – the car has an anti-siphon valve!

Unless you are trying to siphon gas from a really old car, chances are that it has an anti-siphon device. You will need to bypass this if you want to get fuel out of the tank.

What Is an Anti-Siphon Valve in a Car?

There are actually two devices that can prevent you from siphoning gas from a car.  The first is an anti-siphon screen.  It is a mesh screen that prevents you from putting anything solid into the gas tank.  This is typically located higher up in the fuel filler pipe.

The second device is a “rollover valve” located at the tank inlet.  This valve is actually meant to keep gas from escaping the car in event of a rollover but it also prevents you from sticking a siphon hose in the tank – hence why it is often called the anti-siphon valve.

How to Bypass Anti-Siphon Valve

Method 1: Park on a Slope

If the car has an anti-siphon screen but does not have a rollover valve, then you can probably siphon most of the gas with this simple trick.  It works because the anti-siphon screen is usually located quite far down the neck of the fuel filler pipe.

Just park the car on a steep slope so the filler is downhill.  Your siphon hose will be able to reach some of the gasoline to siphon it out.

Method 2: Break the anti-siphon screen

It is possible to break through the anti-siphon screen in a car.  I don’t recommend this because you could end up blocking the fuel outlet if any part of the screen falls into the tank.

You’ll need something long and sharp to puncture the anti-siphon screen.  The problem is that metal-on-metal can create a spark.  And a spark could result in a massive fire!

A good solution is to use copper.  Because copper has high conductivity, it generally will not create sparks.  Copper wire by itself probably won’t be strong enough to puncture through the screen.  One solution is to make a copper ring and solder it to a copper pipe.  You then feed the pipe into the fuel filler tank and use the ring at the end to break the screen.

If the car only has an anti-siphon screen, then you’ll be able to siphon gas after breaking the screen.  But, if it also has a rollover valve, then you’ll need to bypass this too (see method 3).

Method 3: Bypass the rollover valve

Car rollover valves allow gas to enter the tank in one direction only.   Most rollover valves are either ball or butterfly type valves.

In theory, you can bypass the rollover valve with the right tools. In practice though, this is very difficult and time-consuming to do.  If the car has a rollover valve, I’d suggest skipping this method and going straight to method #4 or #5.

To bypass the rollover valve:

  • You will need about 8 feet of ¼ inch plastic hose. It should be stiff but still flexible.
  • Cut the end of the hose at an angle to create a narrow end.
  • Stick the hose into the fuel tank.
  • When you hit the rollover valve, use a twisting and pushing motion. This should get the hose past the valve and into the fuel tank.
  • Attach a thicker hose to the end of the ¼ inch hose.
  • Connect the thicker hose to your bulb siphon pump.
  • It will take about 5 minutes of active squeezing to siphon a gallon of fuel because the hose is so narrow.

Again, this method is a lot more difficult than it sounds, especially since there’s no way to see if the hose is actually getting past the valve.

If you really want to try it, I recommend buying a spare rollover valve and testing it out.  You’ll be able to see what you are doing and figure out the right movements to get the hose into the valve.

Method 4: Disconnect fuel line and drain fuel

Instead of trying to bypass the anti-siphon screen and/or valve, you can access the fuel from the other side of the tank.  To do this:

  • Locate the fuel line.
  • Disconnect the fuel line. You may need a special tool for this (like this). It’s possible to make your own fuel disconnect tool. See this video.
  • Attach a hose to the end of the fuel line. Direct the other end of the hose into your canister.
  • Turn the car on. The fuel pump will cause the gas to flow out of the tank and into the canister.  You’ll need to keep turning the car on/off to keep the gas flowing.
  • If you cannot turn on the car, you can instead jump the fuel pump relay terminals. This can be done with the engine off if you have a jumper.  I haven’t tried this but, according to one source, on Toyotas you can put a paperclip on the test plug in the engine to jump the fuel pump.

Method 5: Use fuel pressure tester with bypass valve

You can use the fuel tank Schrader valve to bypass the anti-siphon valve.  The fuel Schrader valve is used for testing pressure.  Not many cars have fuel line Schrader valves though, so this might not be an option.

If there is a Schrader valve, you will need to get a fuel pressure test kit with a bypass valve (like this one).  Hook this up, put the bypass valve hose in a canister, start the car and then turn the bypass on.   The fuel will flow into the canister.

You have to be able to turn the car on for this method to work. So, unless you also know how to jumpstart a modern car, this is only an option for siphoning fuel from your own vehicle.

Method 6: Drill a hole in gas tank

As a very last resort, you can get gas out of a car by drilling a hole into the tank.  Put a canister underneath the hole and gas will flow into it.

Aside from the fact that this will destroy the fuel tank, there is a huge fire risk when drilling into metal fuel tanks.  The metal-on-metal will create sparks, which in turn can ignite the gas in the tank.  Only do this on cars with plastic (polymeric) gas tanks.

Warning!

With some of these methods for siphoning gas, the car engine needs to be turned on.  It is always a risk to handle fuel while the engine is running.  To stay safe, you should:

  • Use a longer hose. The hose in most siphon kits is only 2-3 feet long. Use a longer hose so you can position the fuel canister further away from the vehicle.
  • Only siphon a few gallons at a time. Drain a few gallons from the tank. Then turn off the car and move the canister out of the way.  This way you won’t have too much fuel sitting near the car at once.
  • Siphon from a cool engine. Wait for the engine to cool down completely before you disconnect anything.

As you can see, siphoning gas from newer cars is fairly complex and can even be dangerous.  Instead of relying on your car gas tank for emergency fuel, it’s smarter to stockpile fuel.

This can also be tricky though because gasoline goes bad. Read this to learn how to store gasoline for emergencies.

Have you ever siphoned gas from a modern car? Let us know your tricks and tips in the comments section below.

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  1. Use an ice pick an puncture the tank in 2 places and have 2 containers ready or more. You can use a sharpened flat head screwdriver as well and make sure to take the fill cap off the vent the flow.

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