Why Does My Toilet Sound Like It Is Flushing on Its Own?

By Chris Deziel

If midnight toilet phantom flushes are giving you nightmares, rest easy -- the little man in your toilet pulling down the flush lever is a figment of your imagination. Really. If you listen carefully, you'll notice that the toilet isn't actually flushing -- it's just the fill valve that's cycling on, and that's probably because the flapper is leaking. The flapper is easy to fix, and it can wait until morning.

So What's a Flapper?

The flapper is the rubber paddlelike stopper over the siphon hole in the bottom of the tank. It's attached to the flush lever by a chain; it flaps up to open the drain when you push and flaps back down when the flush is complete. When it's down, it fits snugly in the drain opening so that the tank can fill and be ready for the next flush.

Red rubber toilet flapper.
credit: cw deziel
A new flapper forms a watertight seal.

Some flappers are plastic with a rubber seal, while others are all rubber, and since rubber tends to deteriorate in mineral-laden toilet tank water, all flappers eventually leak. When it does, the water drains gradually until the level is low enough to trigger the fill valve. If the leak is barely perceptible, it can take hours for the water to drop to that level, and the fill valve may engage at midnight, even though no one has used the toilet since midafternoon.

The Dye Test

Restroom background. Toilet bowl closeup  full of blue water.
credit: mettus/iStock/Getty Images
Use the dye test to verify that the flapper is leaking.

If you're the skittish type, you may need verification that the flapper is leaking to ease your hyperactive subconscious and convince yourself that the phantom flusher isn't real. That's easy to get:

• Drop some food coloring into the tank.

• Avoid using the toilet for eight to 12 hours.

• Look carefully at the water in the bowl. It should be turning the same color.

OK, It's Morning ... Now What?

There's no point trying to repair the flapper -- you can do it, but it's more reliable to spend the $5 or so it takes to buy a new one. To remove the old flapper:

Turn off the water.

Flush the toilet.

Disconnect the chain.

Pull the rubber ears off of the posts on the overflow tube, or slide the flapper up and off the overflow tube, depending on what kind of flush valve you have.

Take the flapper with you to the hardware store to find a replacement. In many cases, you can buy a universal adapter and adapt it to fit your toilet, but some toilets require specific flappers. Replace the flapper by reversing the procedure for removing it.

Wait! My Toilet Doesn't Have a Flapper!

Toilet manufacturers are increasingly including flapperless flush valves in their products, and when one of these leaks, it's for essentially the same reason -- a worn seal. Whether the toilet is a single- or dual-flush, you usually replace the seal by following the same procedure:

Toilet dual flush canister. Top view.
credit: cw deziel
A canister seal can leak -- just like an old flapper.

Turn off the water and empty the tank.

• Disconnect the tube from the fill valve. Also disconnect the flush chain from the canister, if applicable.

• Grasp the top of the canister and turn it counterclockwise to release it.

• Pull out the seal from inside the flush valve and replace it with an identical one.

• Replace the canister and turn it clockwise to lock it in place.

• Reconnect the fill valve tube and turn on the water.