A leaking Kohler toilet class six flush valve may be due to a damaged or corroded flush valve seat. The canister flush valve seat is the base of the unit where the flush valve seal rests. The seal and seat must fit perfectly together in order to function properly. You can repair minor imperfections such as mineral deposits from hard water by buffing the seat with a fine grade steel wool. If the scaring is too deep, replacing the Kohler flush valve seat is the only way to repair the toilet.
Shut off the toilet's water supply and unscrew the supply line from the fill valve. Flush the toilet and continue holding the handle down to remove as much water as possible from the tank. Soak up the remaining water with a sponge or towel.
Disconnect the tank from the bowl by unscrewing the tank-to-bowl bolt nuts underneath the bowl's rim with an adjustable wrench. Lift the tank off the bowl and set it on a bath towel. Peel off the old black foam tank-to-bowl gasket from the locknut on the bottom of the tank.
Unscrew the flush valve's locknut with a large pair of slip joint pliers. Separate the small black rubber fill tube from the top of the flush valve and disconnect the lift chain by hand. Pull the entire flush valve assembly out of the tank. The tank's attachment plate will separate when the valve is removed.
Unscrew the fill tube, the thin plastic tube in the centre of the flush valve, from the flush valve's seat. The flush valve canister and seal will separate with the fill tube.
Install the new flush valve seat using a new shank washer and tank-to-bowl gasket. Reassemble the parts in reverse order. Reconnect the water supply and turn the water on. Flush the toilet several times to assure proper operation.
Kohler flush valve seats, rarely sold separately, are part of the complete canister flush valve kit.
Do not over tighten the tank-to-bowl bolt nuts or the flush-valve locknut.