Sink plunger

A plunger, force cup, plumber's friend, or plumber's helper is a tool used to clear blockages in drains and pipes. It consists of a rubber suction cup with an attached stick (shaft), usually made of wood or plastic. A different bellows-like design also exists, usually constructed of plastic.

For the common plunger, the cup is pushed down against the drain opening, either pressing hard into the drain to force air in, or pushing down until the rubber cup is flattened and then pulling out, creating a vacuum that attracts material. The intent is to loosen or break up a blockage caused by excessive material in the drain.

The cup of a kitchen plunger looks like a rubber ball cut in half with a flared edge, while the toilet plunger's cup looks more like a distorted ball, tapered on one half, with a large hole on the bottom.

A plunger is much more effective with water in the pipe because water does not compress and will thus transmit more of the applied force than air. When a plunger is ineffective, it is supplemented by a chemical drain cleaner (in the case of sinks and tubs) or a plumber's snake (for stubborn clogs or clogs of the main line or toilet).

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Wikipedia