The item can be used to stop the waste of water, which is filling the toilet water tank, in case that both the flushing mechanism (including the gasket), and the faucet malfunction, and the water flow continues into the toilet, even when the faucet is closed.
Please note, that this model may not apply to each and every flushing mechanism. Please, see the photos to see, if your flushing mechanism is compatible with this specific model.
The author marked this model as their own original creation.