How to install a new flush valve assembly black plastic with overflow, outlet and flush opening

make sure it is the correct replace kit. It should not require any force to install.

You need to adjust the float. Or, you can buy the complete inexpensive float valve assembly at Lowes or Home Depot and can install it in less than 5 minutes. Turn off the water supply, drain the tank, sop up the remaining water in the tank or put a pan under the tank opening for the next step, remove the valve assembly and float and install the new valve assembly with the float included. Turn on the water supply and set the water level adjustment valve to about 1/4 inch below the stand pipe overflow drain. This is done by the float assembly. Turn on the water supply. This completes the change-out.

Dont flush untill you have removed the heater control valve because it has a piston and diaphragm setup vacuum on the line will cause the diaphragm to expand and not close causing the valve and hose to fail no matter how tight you clamp it. heater control valve is located at rear of engine bay passenger side near heater core hoses.

Flapper or flush valve needs servicing
First try cleaning minderal deposits from around the valve seat. This can keep the flapper valve from sealing properly and allow water to seap into the bowl. First turn of the water and flush the toilet to empty the bowl. You can unhook the flapper valve to get it out of the way. Using emery cloth scrub the inside of the valve seat to remove the mineral deposits. Next coat the valve seat with petroleum jelly to help the flapper valve make a tight seal. Replace the flapper valve, turn on the water and check to see if the water still leaks.
If the flapper valve is old it may be deformed. In this case you will need to replace it. You can unhook the valve and remove the lift chain from the valve. Be sure to purchase a similar size replacement valve.
If the valve seat is damaged you will need to replace the entire flush-valve assembly. You will need to remove the tank to do this. Be certain to turn off the water supply and flush the tank to drain it. You might also want to place newspaper and towels on the floor to soak up any water that may leak out. Using and adjustable wrench loosen the nuts at the supply tube and push the tube aside. Next, use a flat-head screwdriver to hold the bolts inside the tank still while using an adjustable wrench to loosen the nut on the bottom of the tank. You will then be able to lift the tank off of the bowl. Lay the tank on the newspapers or towels.
To replace the flush-valve assembly first remove the old one by unscrewing the locknut on the bottom of the tank. Use a hacksaw to cut the new overflow pipe to 1/2 ince below the tank top. Put plumber's putty on the washer at the base of the flush-valve assembly and push the assembly against the tank opening, removing any excess putty. Use a monkey wrench to tighten the locknut. Replace the gasket over the locknut and replace the tank on the bowl and reassemble them.
g and adjustable wrench loosen the nuts at the supply tube and push the tube aside. Next, use a flat-head screwdriver to hold the bolts inside the tank still while using an adjustable wrench to loosen the nut on the bottom of the tank. You will then be able to lift the tank off of the bowl. Lay the tank on the newspapers or towels.
To replace the flush-valve assembly first remove the old one by unscrewing the locknut on the bottom of the tank. Use a hacksaw to cut the new overflow pipe to 1/2 ince below the tank top. Put plumber's putty on the washer at the base of the flush-valve assembly and push the assembly against the tank opening, removing any excess putty. Use a monkey wrench to tighten the locknut. Replace the gasket over the locknut and replace the tank on the bowl and reassemble them.

I haven't seen a pink one, but the new gasket should fit over the nut on the new overflow. Keep tightening down the bolts slowly a little bit at a time on each one until the tank doesn't rock. Check on it for a week or two to make sure it doesn't leak. If you don't like the seal that came with the kit, you can buy a different one for a few bucks at the hardware store.

The rubber washer goes to the inside of the tank under the flush valve which gets screwed on with the large plastic nut on the bottom side of the tank. Then the foam gasket fits over the plastic nut which goes into the toilet bowl hole for the water to flow into the bowl. Tank needs to be removed from the toilet bowl.

did you have the tank removed from the bowl?
if you did, there is a rather large nut that holds the flush valve to the tank, fairly simple to reinstall.
if you did not have the tank removed from the bowl, and you pulled up on the overflow tube "round white thing" then you probably broke it. you will need to replace the whole flush valve assembly.
you can get one from your local hardware store. you will also need new tank bolts, and a new gasket that goes between the tank and bowl.

The foam gasket stays on the inside of the tank, the only part that gets pushed through the hole is the hard plastic threaded part, then you add the rubber washer and the nut from underneath.

First things first, remove the fill valve, and the flush handle mechanism. This will give you plenty of room to work with the flush valve. Before installing flush valve lubricate tabs with plumbers grease. Now put on a pair of work gloves, pushed down very hard and turn the tabs should slide easy because of the grease. Remember do not alter the gasket, the gasket needs to be compressed to do its job. I know removing the fill valve and the flush handle seems like a pain, but there is no way to get your hands in the proper position to install the flush valve assembly.

If you purchase the flush valve from Kohler, it comes without instruction. Rotation is the key to removal. First note the exact orientation of the assembly before attempting removal. Unhook the flapper chain and remove the flapper. The old assembly does indeed rotate in either direction for removal. I used a counterclockwise motion. (it was a tough turn, don't break the bottom of the bowl where the valve seat is located.) Then install the new foam gasket on the assembly. The new assembly is replaced in the reverse manner. I removed the new flapper from the flush valve for ease of install. You must put significant downward pressure on the flapper seat while rotation is accomplished. Orient the assembly as was the old one. Replace the flapper, connect the chain and observe the flapper for proper opperation.