Use a small adjustable wrench to disconnect the toilet stop nut (Image 1). Disconnect the tank from the bowl by removing the bolts found inside the bottom of the tank.
Using a large screwdriver to support the head on the bolt, then turn the nut under the tank with an adjustable wrench (Image 2) until it is possible to remove the entire bolt from the tank. Repeat the process on all the bolts.
Disassemble and remove all parts inside the tank.
When replacing the tank to bowl gasket, buy several types of gaskets to match up to the one being replaced. If none of them work, use a 'fit-all' gasket.
Carefully align the valve assembly. Gently push through the hole, then turn the locking ring hand tight (Image 1) to make a good seal.
Use large pliers to fully tighten the seal.
Guide the assembly through the hole, then put the tank seal into place that's located on the ballcock and hand tighten the locking nut. Use a small pair of slip-joint pliers to get a more secure fit (Image 2).
There are 21 pieces to install three tank-to-bowl nuts. Start off with the bolt then slide on a seal. Repeat this process for the other bolts.
It's time for the outside seals. Use the same process as before; squeeze all the rubber seals onto the bolts (Image 1). Once all the inside and outside seals are in place, slide the brass washers on and lock them into place with thinner nuts. Hand tighten; use an adjustable wrench to secure.
Start with the flexible supply line (Image 2). It has a heavy-duty seal that should be hand tightened, then use slip-joint pliers a quarter turn. Slide the handle through the hole and then tighten the bolt.
Don't forget to take the overfill tube and place it back into the hole (Image 3). The overfill tube is what fills up the bowl during the flushing cycle.
Position the tank on top of the bowl. Tighten all of the bolts using small slip-joint pliers and make sure the tank doesn't wobble.
Hold the handle all the way down while the water is filling into the bowl. This will reveal if there are any leaks before the bowl is full of water.
If the seal looks good, let off the handle to allow the bowl to fill up completely. Adjust the water level so it's 1/2 inch below the fill tube.