Tank Fit

Water on the floor

Leak between the tank and the bowl

Water at the back of the toilet base usually comes from one of four places: condensation, the supply line, the tank bolts, or the tank-to-bowl gasket. The bolts and gasket wear out together, so they are replaced as one kit.

Find the source first

Dry everything with a towel. Put food coloring in the tank and do not flush. Wipe a dry paper towel along the supply line and shutoff, under each tank bolt head, and along the seam between tank and bowl.

  • Colored drips at the bolts or seam: tank bolts or gasket.
  • Clear drips at the supply connection: the supply line or fill valve nut (see supply line).
  • Beads of water over the whole outside of the tank in humid weather: condensation, not a leak.
  • Water only appears at the base when you flush: that is the wax ring, not the tank.

Bolts only: do not just crank them

If drips come from a bolt head, snugging the nut a quarter turn can stop it. Overtightening is how tanks and bowls crack. If a quarter turn does not stop it, the rubber washers are done and the kit is the fix.

Replacing the gasket and bolts

  1. Shut off the supply, flush, and sponge the tank dry.
  2. Disconnect the supply line at the tank.
  3. Hold each bolt head inside the tank with a screwdriver and remove the nuts underneath. Corroded bolts may need a hacksaw blade between tank and bowl.
  4. Lift the tank off and set it on a towel.
  5. Remove the old sponge gasket from the flush valve nut on the tank bottom, and clean the bowl inlet.
  6. Fit the new gasket, new bolts with rubber washers inside the tank, and set the tank back.
  7. Tighten nuts alternately, a little at a time, until the tank is level and does not rock. Stop there.
  8. Reconnect the supply, refill, and dye test the seam.

Match the gasket to the tank

Gaskets are brand specific on some toilets: Kohler, TOTO and American Standard often use their own gasket shape, and 3-inch flush valves need a 3-inch gasket. Read the tank stamp and buy by model. If the flush valve nut is cracked, replace the flush valve while the tank is off (see rebuild kit vs one part).
Tank-to-bowl kit (2-inch or 3-inch, by brand)Tank-to-bowl gasket and bolt kittypically $8 to $20
Fits
Two-piece toilets leaking at the bolts or seam, matched to the flush valve size and brand.
Does not fit
One-piece toilets (no tank-to-bowl joint), and generic gaskets on Kohler, TOTO or American Standard models that specify their own.
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FAQ

Why is water leaking between my toilet tank and bowl?

Usually worn rubber washers on the tank bolts or a worn tank-to-bowl gasket. A dye test in the tank shows which.

Can I just tighten the tank bolts?

A quarter turn can stop a bolt drip. More than that risks cracking the tank or bowl; replace the washers instead.

Do I need a 2-inch or 3-inch tank-to-bowl gasket?

It matches the flush valve size. Measure the drain opening or check the model number on the tank stamp.

Is water at the toilet base a tank leak?

If it only appears when you flush, it is more likely the wax ring under the toilet.

Next, in the tank