Turn off the water to the toilet tank by turning off the toilet stop or closet stop, which is by the base. Keep turning the handle clockwise until it shuts off.
After turning off the water, your next step is to drain your tank. To drain the tank, push the handle down and hold it until no more water goes down the hole. At this point, there will be about an inch of water left in the hole. Use a sponge to wipe the remaining water from the tank.
Drain the tank by pushing the handle down and holding it until the water goes all the way down. Hold the handle until no more water goes down the hole. There will still be about 1 inch of water in the tank. Wipe all the water out using a sponge.
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).
To reinstall the tank, position it on top of the bowl. Tighten all the bolts using small slip-joint pliers to ensure the tank doesn't wobble. For the outside seals, squeeze on all the rubber seals of the bolts and slide the brass washers on and lock them in place with thinner nuts. As the tank fills, hold down the handle so that you can see if there are any leaks.
Once your tank is reinstalled, it's time to tighten the water line. First, tighten the line as best you can with your hand. After you have hand tightened your line, use an adjustable wrench to ensure that the water line is secured to the tank. Once you have secured the line, you can safely turn your water back on.
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.