Bilge siphon hose. Whenever the jetpump is pumping (engine running, in the water)... there is a suction created on that hose to suck out any water in the bilge. Clean screen and put end of hose down low where water collects. The middle of this hose needs to run up high (over the engine) to get above the waterline to prevent backflow when engine is off and boat is in the water.