The NDS 4 in. Pop-Up drainage emitters act as the discharge point of a drainage system, opening easily when excess runoff is beyond system capacity to allow water to flow freely from the pipe and away from structural foundations, discharging at a safe location. The cap opens with the hydrostatic pressure of water flowing through the drain pipe, then closes as the flow diminishes. It allows water to be diverted and released to water-safe areas away from structures, erosion-prone landscapes, and poor drainage areas. The NDS pop-up drainage emitter with elbow is an easy, safe, and efficient solution to any drainage needs. Color: Green/Matte.