Your sink is filling with water when you have the water is running? It is because there are small things going down in the pipe.
Here is a product that can prevent this from happening. Just put it in your sink in the kitchen or in the toilet sink.

PETG plastic
Weight: 10g
Inner diameter: 40mm
Outer diameter: 70mm
Height: 7mm

Packet includes:
2 * Sink stop stopper