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How to Test a Toilet for Leaks

By: Danny Lipford
Replacing the rubber flapper valve in a toilet tank to stop it from leaking.

Replacing the rubber flapper valve in a toilet tank to stop it from leaking.

Toilets can develop undetected leaks between the tank and bowl that can waste thousands of gallons of water if not repaired. If you notice your toilet refilling periodically when it hasn’t been flushed, it’s a sure sign your toilet has a leak.

There are two ways to test your toilet for leaks:

  • Toilet Leak Test #1: Remove the tank lid, and pour a small amount of food coloring in the tank to color the water in the tank. If colored water appears in the bowl without flushing the toilet, it indicates water leaking between the tank and bowl.
  • Toilet Leak Test #2: Another way to test your toilet for leaks is by turning the water to the toilet off at the shutoff valve. Remove the lid to the tank and note or mark the water level in the tank. Wait several hours to overnight without flushing the toilet, then check the water level in the tank. If the water level is lower, there’s a leak between the tank and bowl.

To repair a leaky toilet:

  1. Turn the water off to the toilet.
  2. Flush the toilet to empty the water in the tank.
  3. Replace the rubber flapper valve in the bottom of the tank.
  4. Turn the water back on and refill the tank, checking to make sure the tank stops filling before it reaches the top of the overflow tube.
  5. Test the toilet again, using one of the two methods above, to see if the leak has stopped.

Watch this video to find out more.

Further Information

Print   Video Transcript

Danny Lipford: Amelia wants to know, “What could have caused my water bill to triple?”

If you’ve experienced a significant increase in your water bill, this could be the culprit. The toilets in your home account for about 25 to 30 percent of your total water bill. So a small leak here could represent thousands of gallons of wasted water.

Now, the most common problem with a toilet that causes it to use that kind of water is the seal between the tank and the bowl. Now, you can test that a couple of different ways.

First of all, take the lid off the tank, put just a little bit of food coloring in the tank, and if it shows up right away in the bowl, you definitely have a problem with that seal. Another way to check it is just before you go to bed, turn the water valve off for the supply, right at the wall, then the next morning, check the tank. If it’s not full, you have a problem.

The good news, to solve the problem, it’s only about five dollars’ worth of materials, and about ten minutes of your time.



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2 Comments on “How to Test a Toilet for Leaks”

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  • Official Comment:


    Ben Erickson Says:
    July 28th, 2013 at 11:42 pm

    Hi Linda,
    Good idea, thanks for the tip!



  • Linda Cade Says:
    July 28th, 2013 at 1:36 pm

    I wanted to check a leak in my toilet but didn’t have food dye…. I used part of a packet of unsweetened Kool-Aid. I think any unsweetened drink mix would do, as long as it’s a deep color. This worked like a charm…..


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