Suitable for salt or freshwater. Fits flush to the floor (in closed position). Comfortable for barefoot use & self-priming. Designed for neat, through-floor mount. When not in use, the plunger locks down flush with the floor. A simple twist releases the plunger for use. Easy, smooth action giving flow on each stroke. A return spring assists pumping. When finished, press down and twist clockwise to return to the locked position. Recommended where there is sufficient fitting space below the cabin sole.