The stopper in your kitchen sink acts as a valve, controlling the flow of water into the drain. Open, the stopper allows clear passage of water to the drain; closed, it forms a seal around the entrance to the drain. A faulty or damaged stopper fails to do either. A homeowner with modest repair skills can replace a flawed stopper valve in just a few minutes.
Open the cabinet door beneath your kitchen sink to reveal the sink's drain pipe. Clear enough room beneath the sink to allow ample work room.
Turn the retaining nut counterclockwise until loose. Slide the the pivot rod from the side of the drain pipe.
Return beneath the sink, and fit the pivot rod back into the side of the drain pipe.