Every time you flush the toilet, the fill valve opens to allow water to refill the tank to the proper level, then it closes to prevent overflow. This device is crucial for the proper functioning ...

The fill valve is what controls the amount of water that goes into the tank ... is as simple as adding hot vinegar into the tank through the overflow tube and letting it soak for a few hours.

remove the tank lid. Inside you’ll should see the main parts responsible for your toilet's water control: the flapper chain, flapper, overflow tube, a ball float or float cup, and fill valve.