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How to test a toilet for a silent leak

Updated . By the OakTend team.

Close-up of a white toilet tank with a round chrome dual flush button

A silent toilet leak is water slipping from the tank into the bowl past a worn flapper. You cannot hear it, but a few drops of food coloring will show it.

How often
Once a year, and any time the water bill jumps. The EPA says flappers wear out and should be replaced at least every five years.
What you need
Food coloring or a dye tablet, A replacement flapper that fits your toilet, if it fails

Why it matters

The EPA says a worn flapper can silently waste thousands of gallons a year. It shows up only on the water bill, and a new flapper is one of the cheapest plumbing parts in the house.

Steps

  1. Take the lid off the tank.
  2. Add a few drops of food coloring or a dye tablet to the tank water.
  3. Do not flush. Wait 10 minutes.
  4. Look in the bowl. Any color there means the flapper or the flush valve seal is leaking.
  5. Flush right away so the dye does not stain the tank.
  6. To replace the flapper: close the supply valve at the wall, flush to empty the tank, unhook the old flapper and chain, and fit a new one of the same type.
  7. Turn the water back on and repeat the test.

When to call a pro

If color still reaches the bowl with a new flapper, the flush valve seat may be worn or cracked. A plumber can replace the flush valve or the tank parts.

Safety

Skip in-tank tablets that contain chlorine: New York City's water department warns they can eat away at the rubber parts that seal the tank.

Go deeper

General information, not professional advice. Your equipment's manual comes first when it says something different.

Sources

More water heater and plumbing