How do I repair a toilet anti-siphon?

Written by chris deziel Google
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How do I repair a toilet anti-siphon?
A toilet anti-siphon valve protects your drinking water by preventing tank backwash. (toilet bowl painting Gzhel image by Vasily Smirnov from

Modern toilet refill valves have built-in anti-siphon protection. This prevents water from the toilet tank being sucked back into the water supply in the event of a sudden, unexpected reduction in water pressure. If you have an older toilet, the valve may not include an anti-siphon feature, and the only way to get back-flow prevention is by replacing it with one that does. It should have the words "anti-siphon" or "code approved" printed on it. Plumbing codes throughout the U.S. and Canada mandate the use of anti-siphon toilet valves.

Skill level:

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Things you need

  • Phillips screwdriver
  • Valve wrench

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  1. 1

    Examine your leaking refill valve, and attempt to repair it only if you determine that it includes an anti-siphon valve. Otherwise, replace it with a new one.

  2. 2

    Unscrew the ball on the end of the lever arm and shake it. Replace it if there is water inside, then screw it back on and adjust the arm so that it stops the refill valve when the tank is full. If the valve still leaks, you should replace the washer on the end of the plunger.

  3. 3

    Turn off the water to the toilet and flush the toilet to drain the tank. Unscrew the nuts or screws on the top of the leaking valve to remove the plunger. There may be two wing nuts that you loosen by hand, or three Phillips screws that you loosen with a screwdriver.

  4. 4

    Lift out the plunger and remove the washer on the bottom by unscrewing the screw holding it. Slide off the washer around the body of the plunger. Replace either or both of them if they are worn. It's best to take the whole plunger assembly to the hardware store to be sure you get the correct washers.

  5. 5

    Look at the valve seat inside the body of the valve. If it has a square or hex (hexagonal) hole, remove and replace it with a seat wrench, which is available at the hardware store. If it has a round hole, you can't replace it, but you can flush it to remove debris by turning on the water for a couple of seconds before replacing the plunger.

  6. 6

    Screw in a new valve seat, if you are replacing the old one, then slide the plunger back in place and replace and tighten the screws that hold it. Turn the water back on.

Tips and warnings

  • Be sure the refill tube does not extend too far down the overflow pipe. If it does, the force of water from the refill tube can created a vacuum that sucks water down the overflow pipe. This is not dangerous, but it wastes water.
  • Be sure the water in your tank never rises above the top of the refill valve. If it does, it will nullify any anti-siphon guarantee the valve may have.

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