A pop-up waste coupling is a type of drain mechanism typically used in sinks, basins, and bathtubs. It features a stopper that can be raised or lowered to allow water to drain or be retained in the basin. The mechanism is operated by a lever or knob, usually located behind the faucet, which connects to a linkage system under the sink. When the lever or knob is pushed down, the stopper is lifted, allowing water to drain. When pulled up, the stopper closes, retaining the water in the basin.