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How to Test for Toilet 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. Fluidmaster’s 502 PerforMAX Water-Saving, Adjustable Flapper offers a customized flush. You just have to turn the dial left for more water per flush, or right for less, depending on your needs.
  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

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.


Please Leave a Comment

9 Comments on “How to Test for Toilet Leaks”

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  • Official Comment:

    Thomas Boni Says:
    February 15th, 2019 at 9:30 am

    Hi, Darryl!
    Several varieties of aftermarket garage door seals are available. Some screw to the bottom of the door while others slide into a channel built into the bottom of the door.
    The solution will depend on the type of door seal that you currently have and need to replace.
    We recommend photographing your door seal and taking that photo to your local home center for the best match.
    Good luck!

  • Official Comment:

    Thomas Boni Says:
    December 14th, 2018 at 1:32 pm

    Hi, Darryl,

    Thanks for your suggestion! We are always looking for ways to better serve our fans and enhance the television show.
    I have forwarded your message to the “Today’s Homeowner” producer for consideration.

  • Darryl Hill Says:
    December 13th, 2018 at 7:49 pm

    I always watch your shows but I have never seen a show that describe how to change the garage door bottom seal.
    I’ve even checked your website for a video on it but to no avail. I live in waikoloa Hawaii on the Big Island. Also can you show how to measure for the strip.
    Thank you

  • Official Comment:

    Thomas Boni Says:
    December 14th, 2018 at 1:34 pm

    Hi, CF,
    Toilets can absolutely leak slowly at the base. This sounds like a problem with the toilet flange wax ring.
    We recommend using Fluidmaster’s no-wax seal. You can learn more about it here:
    Good luck!

  • Carolyn Freund Says:
    December 13th, 2018 at 7:02 pm

    Can there be a very very slow leak where the toilet bottom attaches to the floor?
    Thank you.
    C F

  • Tom Says:
    September 12th, 2018 at 11:29 pm

    I’ve replaced all the parts in the tank, fill tube with is seal, filler valve, flapper, including the seal between the and and the bowl section. I’ve adjusted it according to instructions. It still drip-leaks. Even if I push down on the flapper, it still leaks. Any advise, please?

  • Anne Brazil Says:
    October 5th, 2017 at 10:13 am

    Hi I have a continuous water leak . My town notified myself about the leak . I put a die pack pill inside tank and my water was b
    Blue so I k ow I have a leak. I went purchased a flapper and replaced that and did die test again water is still blue what Is my next ? I can’t afford a plumber so I’m trying to fix it myself with no help. Almost 60 years old and struggling like most people. Any info would be greatly appreciated . Thank-you Annie

  • 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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How to Test for Toilet Leaks