A duckbill is a one-way valve. They prevent aeration, and reduce fuel slosh noise and are commonly used on the return hose inside fuel tanks to prohibit fuel backflow for fire safety. When used with venturi jet pumps, they prevent air from from entering the vacuum chamber and disrupting the flow path. Secure with a small zip-tie. 

Material: Fluorosilicone
Opening Pressure: 0-1 kPA
Hardness: Shore A70
Inner Diameter: 3/8" (9.5mm)
Height: 0.89" (22.6mm)

Compatible with ALL fuel types