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Home & Daily Life

Fixing a running toilet

Most running toilets come down to a worn flapper or a float set too high. Find out which with a few drops of food coloring, then swap the cheap part.

Easy20 min to doThe price of a replacement flapper

You'll need

  • Food coloring
  • A replacement flapper that fits your toilet (take the old one to the store)
  • A towel

Do it like this

Inside a toilet tankA toilet tank in cross-section. The handle connects by a chain to the flapper, a rubber seal over the drain at the bottom, which is highlighted as the most common fix. On the left is the fill valve with its float. In the middle is the overflow tube. The water line should stop below the top of the overflow tube.Overflow tubeWater line: below thetop of the tubeFloatFill valveChainFlapper (most common fix)Handle
If dye reaches the bowl, it's usually the flapper.
  1. Lift the tank lid and put a few drops of food coloring in the tank. Don't flush. If color shows up in the bowl after 10 minutes, you have a leak (EPA WaterSense). Flush afterward so the dye doesn't stain.
  2. If water is spilling into the overflow tube, the float is set too high. Adjust it down so the water stops below the top of the tube.
  3. If color leaked into the bowl, the flapper probably isn't sealing. Turn off the valve behind the toilet (clockwise), flush to empty the tank, unhook the old flapper and hook on the new one.
  4. Turn the water back on, let the tank fill, and run the dye test again.
Watch out. If the toilet is overflowing, turn the valve behind it clockwise to shut off the water first, then deal with the rest. If you rent, tell your landlord about leaks in writing.

See it done

How to Repair Toilet Tank ComponentsThis Old House · Length 4:24 · 2020

Video blocked on this network? You don't need it. The written steps above are the whole lesson, and the video is extra. Watch it on YouTube later.

If it doesn't work

  • Still leaking after a new flapper? Make sure the chain isn't too tight or too long. It should have just a little slack.
  • Still running with no dye in the bowl? The float or fill valve may need adjusting or replacing.
  • Valve behind the toilet won't turn? Don't force it. Use the main shutoff for the home (Regional Water Providers Consortium) and call a plumber or your landlord.

Good to know

Why bother

The EPA says worn toilet flappers are one of the most common household leaks, and the average household's leaks waste more than 9,300 gallons a year (EPA WaterSense).

It adds up nationwide

Household leaks waste nearly 900 billion gallons of water a year across the country (EPA WaterSense).

Check your bill

The EPA suggests looking at a winter month's water use. A family of four using more than 12,000 gallons a month likely has a serious leak (EPA WaterSense).

Sources

  1. U.S. Environmental Protection Agency Fix a Leak Week
  2. U.S. Environmental Protection Agency WaterSense statistics and facts
  3. Regional Water Providers Consortium Emergency water shut-off

Lesson H4.3 · Last checked October 2, 2026 against the sources listed. See a mistake?