Forespar's vented loop/siphon valve will ensure that fluids do not siphon from tank to tank. Commonly used in marine toilet and engine cooling systems, the valve system incorporated in the top of the loop allows air to enter the line when not in use, yet seals as fluid passes through. Made from molded-in, glass-reinforced Marelon, the valve stays corrosion-resistant after extended use. For added security, the one-way valve is designed to seal properly if particulate matter is present in fluids. 7-3/4"W x 6-3/4"H.