How do toilet plungers work?

Answer 1

While water will compress, it does so very little and so in a confined area, like a drain pipe, acts very much like a solid. When there is a blockage in a line with water backed up behind it, such as a sink drain or toilet, the rubber cup of the plunger acts to make a seal so that when you push on the handle, the water caught between the plunger seal and the blockage is pushed down the drain as if it were solid, thus forcing the blockage down the drain. This often moves the blockage to a larger portion of the drainage system, past the place where it is caught or simply breaks up the blockage so that it can flow down the drainage system.