What you'll need
You probably have these
Tick them off as you find them.
Only if you're missing something
- Universal toilet flapperOnly if yours is warped or fails the color test$5 to $15
- Fill valve kitOnly if it still hisses after you lower the float$10 to $25
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The fix
- 1
Lift the tank lid
Set it on a towel on the floor. It's heavy and it breaks if dropped.
You'll know it's right whenYou can see the chain, the float, and a tall open tube in the middle.
- 2
Check the overflow tube
Look at that tall open tube. See if water is spilling down into it.
You'll know it's right whenIf water is pouring in, your fill level is too high. Go to the next step. If not, skip to the chain.
- 3
Lower the float
Turn the screw on top of the fill valve, or pinch the clip on the float and slide it down. Aim for water about 1 in below the top of the tube.
You'll know it's right whenFlush. The tank refills, then goes quiet.
- 4
Check the chain
Look at the chain from the handle to the rubber flap at the bottom. Leave about 1/2 in of slack.
You'll know it's right whenToo tight holds the flap open. Too loose can get caught under it. A little droop is right.
- 5
Run the color test
Add a few drops of food coloring to the tank. Don't flush for 20 to 30 minutes.
You'll know it's right whenColor in the bowl means the rubber flap is leaking. It needs replacing.
- 6
Swap the flapper
Turn the valve behind the toilet clockwise to shut off the water. Flush to empty the tank, then unhook the old flapper and hook on a new one.
You'll know it's right whenThe new flapper sits flat over the hole with no gaps.
- 7
Turn the water back on
Open the valve and let the tank fill. Flush once to test.
You'll know it's right whenIt fills, it stops, it stays quiet.
Hear that silence? That's your water bill thanking you.
Why it happens
Inside the tank, a rubber flap holds the water in until you flush. Over time that rubber gets warped and stiff from water and cleaning tablets, so it stops sealing. The float can also drift out of place and let the tank overfill into the overflow tube. Neither one is something you did. Toilets wear out quietly.
Edie's tipSkip the bleach tablets in the tank. They can wear out the rubber flapper faster.
What not to do
- Buying the first flapper you see
Most toilets take a 2 in or 3 in flapper. Take the old one to the store to match it.
- Making the chain tight
A tight chain holds the flapper open a crack, so it runs forever.
- Forcing a stuck valve
Old shut-off valves can snap or leak if you crank them. If it won't turn by hand, call a plumber.
- Ignoring it
A running toilet can waste a lot of water every day. It shows up on your bill.
When to call a pro
Call a plumber if the fill valve keeps hissing after you lower the float. Call too if water leaks around the base or tank bolts, the shut-off valve won't close, or the tank is cracked.
Questions
Why does my toilet fill up by itself every few hours?
That's usually a leaky flapper. Water slowly slips into the bowl, the tank drops, and the fill valve tops it up. The color test confirms it.
What if the float fix doesn't stop the hissing?
The fill valve itself may be worn out. Replacement kits cost about $10 to $25 and come with instructions. If that sounds like too much, a plumber can do it quickly.
Is it safe to put my hand in the tank?
Yes. Tank water is clean water from your supply line. Rinse your hands after if it makes you feel better.
Written by the DIY Project team and checked against manufacturer instructions. How we check
Updated October 2, 2026.
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