Airtight Seal

• A rubber suction pad is shaped the same way the sink drain is shaped. Thus, when you put it onto the sink, it creates an airtight seal. This airtight seal stops water and debris from moving back out of the sink; as you move the suction pad back and forth over the drain, it breaks up the clog into smaller pieces so that the pieces can move through the pipes.
  
  

Shape of Drain

• For the airtight seal to be effective, the plunger must be the same shape as the drain. Check your sink drain and compare it to the shape of your rubber plunger. You can often change the shape of a rubber plunger to match the shape of the sink drain. For example, if your plunger has rubber flanges and your drain's shape is flat, you can tuck the flanges inside the plunger to make it flat.
  
  

Types of Clogs

• Rubber plungers only work on clogs that can be broken up into smaller pieces, such as dirt. If your sink is plugged up because your nephew threw a toy down the drain or you have a grease clog, plunging won't really do much because these types of clogs can't be broken up into small pieces. In fact, trying to plunge this kind of clog might make it worse. Plungers sometimes work on hair clogs, so you can try plunging first, but if the plunger isn't sufficient to break up a hair clog you may need to use a snake or auger instead.
  
  

Move Water

• Although rubber plungers form an airtight seal, they work by moving water, not air. Once you have formed your seal, moving the rubber suction pad up and down will force water through the drain, thus breaking up the clog. You need a certain amount of water in the sink to break up clogs using a rubber suction pad.