Installing one of our vented loops will ensure that fluids will not siphon from tank to tank. Vented loops are commonly used in the marine toilet system and engine cooling system. The simple valve system incorporated in the top of the loop allows air to enter the line when not in use, yet effectively seals as water or other fluid passes through. Molded in Marelon®, neither vent nor loop will corrode. The duckbill one way valve is designed to seal properly if particulate is present in fluids. The new MF-846 vent barb assembly option can be used in lieu of the standard MF-841 cap/duckbill. This option allows venting to the outside of the hull via a 1/4" (6.35mm)hose.