Vented loops are vital components to reduce the risk of sinking or flooding. The glass reinforced composite Marelon(TM) Vented Loops allow air to enter the lines preventing that dangerous back siphoning effect. Use above the waterline on your head discharge system, bilge pump, the engine, gen-sets, air conditioners, ballast tanks or other equipment. Vented loops help make sure your boat stays afloat after the pumps are turned off. Model MF845 Hose 1/2" Barb Size 4-1/4" W x 5-1/4" H