Why does my toilet leak from the tank when I flush?

Korky describes the symptom this way: water pooling on the floor, leaking from the tank bolts, or leaking around the tank base. Its fix is to replace the tank-to-bowl gasket and hardware. Check three other spots before you order parts, though.

• The lever or lid area. Fluidmaster says that if the toilet keeps running and you see water on the floor, turn off the water and look inside the tank to see whether it is coming from the lid or the tank lever area. Its remedy there is to replace the fill valve and the flush valve, because the flush valve may have the wrong height or may be blocking water from draining into the bowl.
• The bottom of the tank at the bolts. Fluidmaster's step for water coming out the bottom of the tank is to change the tank bolts and washers.
• The base of the toilet. Water at the floor line is a different seal, the one under the bowl. It is covered in what else besides the flapper can cause a leaky toilet.

The gasket is the watertight seal between the tank and the bowl. Korky says that over time, the weight of the tank and water can compress and wear down the gasket, and that normal use can also make the tank shift slightly, especially if someone leans back against it or it gets bumped while cleaning. That movement can weaken the seal. As the gasket compresses, the tank bolts may also loosen. Tightening the bolts may fix the problem, Korky says, but do not overtighten them or let the tank touch the bowl, because the porcelain can crack.

Sometimes, and it takes two minutes. Shut off the supply valve and flush so the tank is mostly empty. Then tighten the nuts under the tank a little at a time, alternating sides. Korky recommends alternating when tightening because it keeps the tank level and stable, and says that having a partner apply even pressure to both sides compresses the gasket evenly. Go snug, not hard. If the leak is still there after a gentle snug, the gasket or the stack of washers is the problem.

A common reason a new gasket still drips is the washer order. Fluidmaster's recommended order for a tank-to-bowl bolt, from the top, is the bolt head, a rubber washer, the tank, an optional metal washer and thin metal hex nut used only if there is a gap between tank and bowl, the toilet bowl, a rubber washer, a metal washer and a metal hex nut. Its warning is capitalized for a reason: do not use a metal washer directly under the bolt head inside the tank, because it will cause a leak. For Kohler 3-bolt tanks, Fluidmaster recommends Kohler's triangular tank-to-bowl gasket and bolt kit.

Korky's steps, in short:

1. 1Shut off the supply, flush, and sponge out the remaining water.
2. 2Disconnect the supply line at the tank and remove the old bolts, washers and nuts.
3. 3Lift the tank off, set it on the closed seat, and remove the old gasket.
4. 4Place the new gasket over the mounting nut threads of the flush valve.
5. 5Reset the tank, attach it with the bolts, rubber washers, washers and hex nuts, and tighten alternating sides while someone presses down to keep it level.
6. 6Reconnect the supply line by hand only, with no sealant or tape, turn the water on slowly and watch the joint while the tank refills.

Gaskets come in two sizes, standard 2-inch and large 3-inch, so match the one you have. Korky also notes that since removing the tank is not routine, you might consider replacing everything in the tank at the same time.

If the porcelain is cracked, the bolts are seized, the tank will not sit level, or the leak returns after a new gasket, have it checked. A cracked tank generally means replacing the toilet. HQ Plumbing and Air handles toilet repair around the Valley, with the price given before work begins. Kohler also notes a separate flush valve gasket where the flush valve meets the bottom of the tank and recommends replacing it when you replace a worn flapper or canister seal, so mention a drip at that joint when you call.