Around the house · Some practice · about 30 minutes
Fix a Running Toilet
A toilet that keeps running, or refills on its own, is quietly pouring water and money down the drain. A worn flapper alone can silently leak thousands of gallons a year. Most fixes happen inside the tank, with cheap parts and no special tools.
When to teach it: Watch from about 7, help from about 9, do it alone from about 12.
You'll need
- Food coloring or a toilet dye tablet
- An old towel (to set the tank lid on)
- Your phone, to photograph the old flapper
- A replacement flapper that matches your toilet (if needed)
- Rubber gloves (optional)
Before you start
- Before you replace any parts, close the toilet's shutoff valve by turning it clockwise, then flush to empty the tank.
Step by step
Tick each step as you go if you like; ticks stay on this device.
Physics
How it works: Floats, valves, and the siphon
The tank stores water for the next flush. When you push the handle, a lever lifts the flapper, and tank water rushes into the bowl.
The bowl drains through a curved pipe called the trapway. The rush of water fills it and pushes out the air, and that change in pressure starts a siphon. The siphon pulls water and waste down the drain until air gets back in and breaks it, which is the gurgle at the end of a flush.
As the tank empties, the float drops and opens the fill valve. Water pours in and the float rises with it. It floats because water pushes up on it with a force equal to the weight of the water it pushes aside. At the set level, the rising float shuts the valve.
If the flapper doesn't seal, water trickles into the bowl, the tank level slowly drops, and the fill valve turns on again by itself. That's why a worn flapper can make a toilet seem to flush or refill on its own.
buoyant force = weight of the water the float pushes aside
Try it: Push an empty, capped plastic bottle down into a sink full of water. Feel it push back. The deeper you push, the more water it moves aside and the harder it pushes up, until it's all the way under.
Keep learning: Science
Teaching it to your kids
- Let your child do the dye test. It feels like a science experiment.
- Flush with the tank lid off so they can watch the flapper, chain, float, and fill valve move in order.
- Leak math: EPA says an average home's leaks can waste more than 9,300 gallons a year. Divide by 365 to find about how many gallons a day that is (about 25).
- Bring them along to the hardware store to match the flapper.
Tips
- Do the dye test at least once a year.
- EPA WaterSense suggests replacing the flapper at least every five years.
- When buying a flapper, check its width and whether it has a foam float. Take the old one or a photo with you.
- Mark the water line in the tank with a pencil before you adjust the float, so you can compare.
Common mistakes
| Mistake | Instead |
|---|---|
| Chain too tight, so the flapper never fully closes. | Leave a little slack so the chain rests without lifting the flapper. |
| Chain too long, so it gets caught under the flapper. | Hook it to a different link to shorten it. |
| Water level set too high, so water trickles down the overflow tube. | Lower the float until the water stops about 1/2 to 1 inch below the top of the tube. |
| Buying a flapper that doesn't match. | Take the old flapper or a photo to the store and match it. |
When to call a pro
- If the toilet keeps running or won't flush after these fixes, contact a local plumber.
Sources
Free how-to guides for families, with nothing to earn, pass or send in. They follow U.S. rules and sources; your owner's manual, product labels and state and local rules come first.