Stop Toilet Tank-to-Bowl Leaks (Gasket)

End that annoying drip between the tank and bowl by replacing the tank-to-bowl gasket and bolt washers.
Difficulty: Moderate
Success Rate: 80%
Cost: $8 - $20
Estimated Timeline: 30–60m
Turn Off Water: Yes
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Tools Needed:

  • Adjustable wrench

  • Deep socket or box wrench (for tank bolts)

  • Flat/Phillips screwdriver

  • Small wire brush or old toothbrush

  • Utility knife or scraper

  • Sponge and small bucket

  • Old towels

Materials / Parts:

  • Tank-to-bowl gasket (match brand/size: doughnut gasket)

  • New tank bolts, nuts, and rubber washers (set)

  • Plumber’s grease

  • White vinegar (for mineral cleanup)

  • Optional: new fill valve shank washer (if worn)

Safety Warnings:

  • Porcelain can crack—use gentle, even pressure.

  • Never overtighten tank bolts.

  • Shut off water and unplug nearby outlets if using a work light.

Test & Verify:

  • Dry all joints; wait 2–3 minutes and recheck for moisture.

  • Gently press the tank corners; it should not rock.

  • Flush twice and inspect under the tank and around bolts.

Cleanup & Disposal:

  • Wipe away mineral residue and drips.

  • Dispose of old gasket and washers.

  • Reinstall the tank lid and stow tools.

Pre-Checks:

  • Confirm leak source: under the tank at the bowl joint or from the tank bolts.

  • Check for hairline cracks in the tank or bowl (if cracked, do not proceed).

  • Note brand/model; buy the correct gasket and bolt kit.

Step-By-Step Instructions:

  1. Turn off the shutoff valve. Flush to empty the tank. Sponge out the remaining water.

  2. Disconnect the fill line at the tank. Place a towel to catch drips.

  3. Remove the tank lid and set it safely aside.

  4. Hold the tank bolt head inside the tank with a screwdriver while loosening the nut below with a wrench or deep socket. Remove both bolts and nuts.

  5. Lift the tank straight up. Set it on a towel on the floor or across the bowl if stable.

  6. Peel off the old doughnut gasket from the flush valve outlet. Scrape mineral crust from the outlet and the bowl inlet. Brush clean; wipe dry.

  7. Inspect the flush valve shank washer inside the tank; replace if deformed or cracked.

  8. Lightly grease new rubber washers. Insert each tank bolt from inside the tank: rubber washer inside against porcelain, then metal washer and nut beneath later.

  9. Press the new doughnut gasket firmly onto the flush valve outlet—seated flat and even.

  10. Set the tank carefully back onto the bowl, aligning bolts through the bowl holes.

  11. Hand-thread the nuts under the bowl. Tighten each nut a few turns at a time, alternating sides, until the tank sits level and stable. Stop when snug; do not force.

  12. Reconnect the fill line. Turn on water. Let the tank fill.

  13. Check for leaks at bolt holes and around the gasket. If any seepage, give each nut a tiny additional turn—alternating—until dry.

When to Stop & Call a Pro:

  • Tank or bowl shows cracks or wobbles even when nuts are snug.

  • Bolt or nut is rust-welded and begins to spin the porcelain seat.

  • Persistent leaks after gasket and washer replacement.

Common Mistakes:

  • Overtightening bolts and cracking the tank.

  • Placing metal washers directly against porcelain inside the tank (rubber must contact porcelain).

  • Mis-seating the doughnut gasket so it pinches or gaps.

  • Ignoring a worn fill-valve shank washer that leaks down the bolt line.

Troubleshooting:

Q: Water still drips from a bolt.
A: Loosen, re-seat the rubber washer inside the tank, add a light coat of grease, and retighten evenly.

Q: Leak only happens during or after a flush.
A: Doughnut gasket may be misaligned; lift tank, re-center gasket, and re-seat.

Q: Tank rocks after assembly.
A: Loosen and re-center the tank; tighten nuts alternately until level and solid. Add nylon spacers if the bowl surface is uneven.

Q: Nuts bottom out but the bolt spins.
A: Replace with a new brass or stainless bolt kit; corroded hardware won’t seal.