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Fix a toilet that leaks from the tank

We'll confirm the leak is from the tank, check the bolts and gaskets, and replace the flush valve gasket or fill valve—or tell you when to call a plumber for a cracked tank.

Troubleshooting · Home plumbing
30–60 min
What you'll need
  • Flush valve gasket kit (spud gasket)
  • Fill valve replacement kit (if needed)
  • Wrench or pliers for tank bolts
  • Towels or rags
Step 1 of 9

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Steps

Goal: Confirm the leak is from the tank, then fix it by tightening bolts or replacing gaskets.

  • Wipe the tank dry and watch where water appears. Tank leaks drip onto the floor or cause constant refilling; base leaks pool at the floor.
  • Good: Leak is from the tank. Proceed to Check tank bolts first.
  • Bad: Leak is from the base or supply line. See the appropriate guide.

Check tank bolts first

Goal: Rule out loose tank bolts before removing the tank.

  • Look inside the tank. The two tank bolts secure the tank to the bowl. Tighten them alternately—a quarter turn each—until snug. Do not overtighten.
  • Dry the tank and turn the water on. Wait a few minutes.
  • Good: No more leak—bolts were the cause. See Verification.
  • Bad: Water still seeps—proceed to Replace flush valve gasket.

Replace flush valve gasket

Goal: Replace the worn flush valve gasket that seals the tank to the bowl.

  • Shut off the water. Flush and sponge out the tank.
  • Unscrew the tank bolts and lift the tank off the bowl. Set it on towels.
  • Remove the old flush valve gasket from the flush valve. Clean the mating surfaces.
  • Install a new gasket per the kit instructions. Reinstall the tank and tighten the bolts alternately.
  • Reconnect and turn the water on. Check for leaks.
  • Good: No more leak. See Verification.
  • Bad: Leak continues—check the fill valve or call a plumber.

Replace fill valve

Goal: Replace a faulty fill valve that leaks or does not shut off.

  • Shut off the water. Drain the tank. Disconnect the supply line from the fill valve.
  • Remove the locknut under the tank and pull out the old valve. Install the new fill valve per the kit instructions.
  • Reconnect the supply and adjust the water level. Test for leaks.
  • Good: Fill valve works with no leaks.
  • Bad: Leak continues or tank is cracked—call a plumber.

When to get help

Call a plumber if:

  • The tank is cracked (visible crack in the porcelain).
  • The leak continues after replacing the gasket and fill valve.
  • You are not comfortable removing the tank.

Verification

  • No water dripping from the tank or tank-bowl joint.
  • Tank fills and shuts off properly.
  • No leaks at the supply connection.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm leak location Verify the leak is from the tank, not the base or supply line.
  2. Tighten tank bolts Check and tighten tank bolts; do not overtighten.
  3. Replace flush valve gasket Remove tank, replace gasket, reinstall.
  4. Replace fill valve If the fill valve leaks or does not shut off, replace it.
  5. Call a pro Tank cracked or leak persists—call a plumber.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Whether the leak is from the tank, base, or supply line
  • Tank bolt tightness
  • Flush valve gasket and fill valve condition
  • Steps already tried

Is the leak from the tank?

Tank leaks drip onto the floor or cause constant refilling. Base leaks pool at the floor; supply leaks drip from the connection.

Wipe the tank dry. Watch where water appears. Good: water drips from tank or tank-bowl joint, or tank constantly refills—tank leak. Bad: water pools at base or drips from supply—different guide.

Yes No

You can change your answer later.

Are the tank bolts loose?

Loose tank bolts can cause leaks at the tank-bowl joint. Tighten alternately; do not overtighten.

Look inside the tank. Check the two tank bolts that secure the tank to the bowl. Tighten alternately—a quarter turn each. Do not overtighten. Good: bolts were loose—dry and test. Bad: bolts already snug—gasket or fill valve likely failed.

Yes No

You can change your answer later.

Does the leak stop after tightening?

Dry the tank and wait. Run water and observe.

Dry the tank. Turn water on. Wait a few minutes. Good: no more leak—fixed. Bad: water still seeps—replace flush valve gasket or check fill valve.

Yes No

You can change your answer later.

Is the leak at the tank-bowl joint?

Water seeping between the tank and bowl usually means a failed flush valve gasket.

Check where the water seeps. Tank-bowl joint: replace the flush valve gasket. Fill valve area: replace the fill valve. Crack in tank: call a plumber—tank must be replaced.

Tank-bowl joint Fill valve or other

You can change your answer later.

Replace flush valve gasket

Shut off water. Drain tank. Remove tank from bowl. Replace flush valve gasket. Reinstall tank. Tighten bolts alternately. Test.

Done

Does the fill valve leak or not shut off?

A faulty fill valve can leak at its base or cause constant running.

Check the fill valve for leaks at its base or overflow. If it leaks or does not shut off, replace it with a universal fill valve kit.

Yes No

You can change your answer later.

Replace fill valve

Shut off water. Drain tank. Remove old fill valve. Install new one per kit instructions. Reconnect supply. Adjust water level. Test.

Done

Leak fixed

The leak stopped after tightening the bolts. Monitor to confirm.

Done

Call a plumber

Call a plumber if: the leak is not from the tank; the tank is cracked; or the leak continues after replacing the gasket and fill valve.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why does a toilet tank leak?
Common causes: loose or corroded tank bolts, a worn flush valve gasket (spud gasket), or a faulty fill valve. Tank bolts and gaskets seal the tank to the bowl; when they fail, water leaks out.
Can I fix a tank leak myself?
Yes. Tightening tank bolts and replacing the flush valve gasket or fill valve are DIY tasks. If the tank is cracked, call a plumber—the tank must be replaced.
When should I call a plumber for a tank leak?
Call a plumber if the tank is cracked, the leak continues after replacing gaskets, or you are not comfortable working inside the tank.

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