Slow filling toilet tank - American Standard 4021 White Cadet 3 Toilet Tank Lid

Toilet tank won't fill up or is slow to fill. The most common reasons for a valve to slow down or no longer fill the tank after the flush are debris issues and the length of time a valve has been in use. ... Valves in use for a period of 7 years or more can have their working parts start to wear out. 1.
https://www.fluidmaster.com/toilet-problems/remove-fill-valve-cap-replace-seal-toilet-wont-fill-slowly-filling-tank/

I think it's not a wise decision to clean a toilet fill valve, rather than buy a new toilet fill valve and replace with the old one.

Thanks.

replace float assembly

In this toilet there is a flapper valve that blocks the hole for the water to transfer from the tank to thebowl. If you fill the tank and water is leaking into the bowl put your hand in the tank and apply alittle pressure to the flapper, the leak should stop. You can buy replacement parts for this toilet at Home depot or Lowes they carry universal lits that are perfect for this issue.

The inlet feed that fills the toilet is blocked slow to fill needs cleaning out .

Is the flapper valve slow to return to the closed postion allowing water to flow through the flush valve? Make sure the toilet flapper is moving freely and is sealing properly against the flush valve. If there is no lengthy or continual water flow in to the toilet bowl then this is not the problem.

Is the water valve on the water fill line to the toilet tank fully open? This may seem silly but it could be this simple.

Check to make sure your fill valve is opening fully. If you have an older toilet there may be some deposits that need to be cleaned way to allow free movement.

If toilet does eventually fill to the desired level, there is no leakage, water valve on fill line is fully open and fill valve is opening fully then recommend you shut off water supply, drain toilet and disconnect water fill line from the water valuve and toilet tanke to make sure there is not a blockage. If the water line and connections are clear you may need to remove the fill pipe in the tank and check for blockage. If this is very old, conisdering the cost and effort, it may be simpler to replace at this time rather than trying to extend the life.

The fill level can be adjusted by either lowering the filler valve column or bending the filler arm down. The adjustment method is dependent on the type of filler valve. Be cautious not to allow the fill level to go above the designated fill line.

Adjust the float in the tank of the toilet.

Okay Howard. It seems that the fill or float valve inside the toilet tank needs to be replaced. If you have a pair of channel locks / large pliers and some patience, you can do this yourself and save $ on a service call. This Solution is providing that you have good water pressure everywhere else in the house. First turn off the water on the supply line going to the tank. Flush the toilet (with the water off) to empty the tank. Take a towel / sponge / or wet vac to remove any remaining water. Remove the nut on the underside of the tank that holds the float / water supply to the tank. Now that you have the water float removed you can go to your local hardware store / Home Depot / or Plumbing Supplies Store and get a new fill valve. There are different kinds but they all do the same thing, fill your tank. I use a Fluid Master, But you may have to use one like you have. The Store will assist you. They are only about $10 - $15 Bucks or so.......Install the new float according to directions.....It is pretty simple. Insert your new float stem into the hole with the proper rubber washers and tighten carefully for a good seal. Insert the new black hose into the overflow tube and you are in business. You will have to adjust the water level to about a 1/4 Inch below the overflow tube for a good flush!!! I hope this helps you with the slow tank fill.............Joe

REMOVE FILL LINE FROM VALVE. HOLD IN BUCKET AND TURN WATER ON, IF GOOD PRESSURE REPLACE COMMODE FILL VALVE. IF BAD PRESSURE CHECK FOR BLOCK ON LINE IT MAY HAVE SEDIMENT ON THE FILTERS.