What to Do When the Toilet Flushes by Itself

A rubber toilet flapper with the flush chain still attached.
  • 1-2 hours
  • Intermediate
  • 20-30
What You'll Need
Food coloring
Universal rubber flapper
Sharp knife
What You'll Need
Food coloring
Universal rubber flapper
Sharp knife

Most homeowners have encountered this eerie phenomenon at some point: it’s the middle of the night, maybe you’re the only one at home, and all of a sudden, the toilet flushes—all by itself. Creepy? Yes. Is there a ghost in your bathroom? Probably not. In fact, the underlying cause of a mysteriously self-flushing toilet is typically something far more mundane: a warped flapper—the rubber plug that lifts when you flush to allow water to flow from the tank into the toilet bowl and then closes to keep the water in the tank.

If the plug gets warped, cracked, or somehow shifts out of place, then water will be able to continually run from the tank into the toilet bowl, causing a perpetual, noisy, and water-wasting flush. Luckily, this is an extremely cheap and easy fix that you can quickly do yourself. Just keep reading to learn how.

Step 1 – The Food Coloring Test

Nine times out of ten, a self-flushing toilet is caused by a flapper gone wrong, but just to make sure nothing else is going on in your toilet, you can do this easy test. Simply drop a few drops of food coloring into the tank water and wait a few minutes. If the coloring appears in the toilet bowl, then you know that water from the tank is leaking into the bowl, and the flapper needs to be replaced.

Step 2 – Get a New Flapper

Go to the hardware store to get a universal rubber flapper, which can be used in any model toilet. This part is very cheap and very easy to obtain. However, you will probably need to trim off some extra material to perfectly match your particular tank. Use a sharp knife to carefully trim away any excess rubber.

Step 3 – Cut the Water

Turn the water valve to your toilet off and let the tank drain before you get started. Trying to undertake this operation under water is even trickier than it sounds.

Step 4 - Remove the Old Flapper

The old flapper will be connected to the flush chain. Untie or cut the chain to remove it, and take note of this flapper’s condition. If the rubber is rippled or warped, it was probably damaged by bleach or blue water tablets. Professionals strongly advise against using those products in your toilet tank because they will damage any rubber parts in a short amount of time.

Step 5 – Install the New Flapper

Hook the sides of the new flapper to the two pegs that are located on the sides of the overflow tube at the bottom of the tank. Make sure that the flapper can go up and down freely, and that when it is in the down position, it fits completely into place and there are no gaps between the rubber flapper and the tube. You can use the food coloring test again to be certain.

Step 6 – Connect the Chain

Connect the chain that is attached to the flush handle to the top of the flapper. Make sure that the chain isn’t too long or too short so the flapper operates properly.