My bathroom has been acting funny for some time. Water would not stop running from the fill valve initially. I noticed the old fill valve had a bended holder arm, so the float couldn't stay flat. I thought it was a fill valve problem, so I replaced the fill valve. After the replacement, water still runs into the water tank about every 5 mins, which is arguably better than before. Last night, I put food coloring in the water, and turned off the valve. This morning, the water in the tank is almost all gone, and the water in the toilet bowl is red, meaning water went from the tank to the bowl somehow.

I don't see any visible water flow that goes into the bowl. I'm wondering if I should definitely change the flapper, or if there is anything else I should check first.

2 Answers 2


If there's no red water on the floor then the flapper is the most likely problem. Run your finger over the plastic rim that the flapper sits on. It should be very smooth with no ridges or cracks. If it's good, then replace the flapper. There only a few bucks at your home store and only takes a few minutes to replace.

  • 4
    ...and if the rim is not smooth or is cracked, it's a bigger job but still not terribly expensive to replace the seat as well as the flapper (some disassembly required, which is what makes it a bigger job.) But usually just replacing the flapper is adequate. Be sure to get the right size - measure carefully, or take it with you to the store.
    – Ecnerwal
    Aug 28, 2020 at 13:30
  • @Ecnerwal Nice addition.
    – JACK
    Aug 28, 2020 at 14:15

Flappers tend to deteriorate over time, usually because of their constant interaction with in-tank cleaning products and chemicals found in the water. They can cause the flapper to warp, crumble, and eventually lose its seal over the flush tube, allowing water to leak through.

There’s a very simple test to tell if your flapper is broken. Add a few drops of food coloring to your toilet tank. You can also use a dye tablet specially designed for this purpose. Wait about 15 minutes after adding the dye. If there’s a water leak, you’ll see the color inside the toilet bowl.

  • 5
    I'm unclear what use an answer proposing that the person asking the question do what they already did and had results from stated in their question is...
    – Ecnerwal
    Aug 28, 2020 at 13:32

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