Vented loops are vital components to reduce the risk of sinking or flooding. The glass reinforced composite Marelon™ 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