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If you discover you have a leak in your toilet, don't wait to get it checked out. As much as 80,000 gallons of water can be wasted each year by an undetected toilet tank leak. That’s more than 200 gallons of water going down the drain each day. Watch this video to help diagnose why your toilet is leaking … and how to fix it.

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Did you know that as much as 80,000 gallons of water can be wasted each year by an undetected toilet tank leak? That’s more than 200 gallons of water going down the drain each day. It’s not good for the environment and it’s not good for your wallet, either. The good news is that it’s usually an easy problem to fix yourself.

Today, I’ll give you the project basics that address the most common problems with toilet tank leaks to help you get started before you head to your local independent home improvement retailer. That’s where you’ll find everything you need, including the tools and materials, , and the right know-how, to complete this project on your own.

There are two common problems that generally cause a toilet to leak-either a problem with the flush valve which looks like this) or a problem with the refill valve (which resembles what I’m holding here).

Since minor leaks many times go unnoticed, an easy way to determine if your toilet leaks is to pour some food coloring or blue laundry fabric softener into the toilet tank when it is fully refilled after a flush. Give it a couple minutes and then inspect the toilet bowl for signs of color. If the water in the bowl is blue, you know there’s a leak.

But before we start troubleshooting whether your leak is coming from a flush or a fill valve (or a specific component), if the internal parts of your toilet look like they were made twenty years ago it will save you time and money in the long run if you replace all of the toilet tank components at once. It doesn’t take that much more time, and most toilet repair parts manufacturers make complete replacement kits with everything you need for around $20.

You’re also going to need some tools to complete this project, so be sure to click the Tools and Materials checklist button to for a complete listing of everything you need.

If you discover you have a leak and the parts in your toilet tank look relatively new, then you should first determine if your toilet problem is with the flush valve or the fill valve. This takes a little more investigating, so let’s get started.

The most common cause of a leaking toilet tank is when the flapper fails to seat properly and form a tight seal against the valve seat. This lets water leak from the tank into the bowl. It may be caused by the flapper being out of position. It might also be caused if there is a mineral build-up on the bottom of the flapper that prevents it from "seating" properly. If you see a scaly build-up on the bottom of the flapper, shut off the water and drain the tank by holding down the flush lever until the tank is completely drained. You can remove the scaly buildup with steel wool or fine sandpaper. You can also buy a new replacement flapper for a few dollars.

As the water leaks out of the tank and into the bowl, it is then replenished by the fill valve, causing a continuous flow of wasted water. To check for this, first shut off the water supply to the toilet. Mark the water level in the tank with a pencil or marker, then check it again in 10 or 20 minutes. If the water level has fallen below your mark, the flush valve is leaking. If not, the flush valve did not leak, and you know that any leaks are being caused by the fill valve.

If the fill valve isn’t working properly, the tank will generally overfill through the overflow tube, and the excess water will continue to run into the toilet bowl. This is usually either caused by a waterlogged float or when the water level is set too high. A good rule of thumb is to set the water level about 3/4" below the top of the overflow tube.

If your fill valve has a threaded shank to adjust the water level, push the lock ring up and turn the shank to adjust the height, which will then adjust the water level.

If you have questions about this or any other home improvement project, be sure to read our list of Frequently Asked Questions for this video. And be sure to print out our Project Instructions, which includes a Tools and Materials checklist, before visiting your local independent home improvement retailer. That’s where you’ll find all the products and helpful advice to complete your project. If you’re not sure where to find your local store, check out our Store Locator.

Good luck with your project and thanks for watching

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  1. 1.remove lid

    Remove lid from tank.

  2. 2.drop in food coloring

    Pour several drops of food coloring or a cap full of blue fabric softener into the tank.

  3. 3.wait

    Wait 10 minutes.

  4. 4.inspect water

    Inspect water in bowl to see if there any signs of color from fabric softener or food coloring. If so, the toilet has a leak.

  5. 5.shut off water

    Shut off water to toilet.

  6. 6.mark with pencil

    Mark water level in tank with marker or a pencil.

  7. 7.wait 10 minutes

    Check back after 10 minutes to see if water has fallen below mark. If so, the leak is coming from the flush valve. Watch the video Installing a New Flush Valve for more information.

  8. 8.if not, check overflow

    If not, check to see if the leak is coming from the fill valve by examining overflow tube to see if water is running into tube. If so, watch video Installing a New Fill Valve for more information.


Project Faqs « back to project

I think my toilet may be leaking. What should I do?

The most likely cause is that your toilet’s flush valve is leaking through the flapper, letting water continue to drain from the tank down into... More »


How do I test my toilet flapper for leaks?

Test your toilet flapper by pouring a bit of food coloring into the tank, then check back in 15 minutes to see if the water in the bowl has changed... More »


Why is water leaking from the base of my toilet?

Most likely the wax ring at the base of your toilet has failed. To replace it you will need to loosen the bolts that hold the toilet to the floor,... More »

I think my flush valve is leaking, is there a way to fix this without removing the tank from the bowl?

Maybe. Start by checking the flapper, which is the rubber and plastic assembly piece that is attached to the chain. When the tank lever is pressed,... More »

How do I test to see if water is leaking from the tank into the bowl?

After flushing the toilet, let it refill. Now put a few drops of food coloring into the tank. If the color appears in the bowl after a few minutes,... More »

What do I need to do to repair my leaking faucet?

Is it leaking from the handle or out the spout? Most faucets are washer-type, and if these are leaking from the spout, you will have to replace the... More »

My toilet is constantly running causing ripples in the bowl. What’s wrong?

Either the float on the fill valve is stuck or it is set too high, causing water to overflow from the tank into the bowl through the overflow tube.... More »

How do I adjust toilet water level?

To adjust the water level on a toilet with modern tank components, there is a lock ring or pinch clamp that allows you to raise or lower the float... More »

How high should the water level in the toilet tank be?

It needs to be high enough for complete flushes, but it should be below the top of the overflow pipe. The tank should have a colored or molded water... More »

Can I test to see if the leak is coming from the refill or the flush valve?

Yes. Shut off the water supply to the toilet. Mark the water level on the inside of the tank with a pencil. Check the water level in 10 or 20... More »

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