One-Way Check Valve
WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.
One-way check valve is located on top of fuel tank. Note direction of valve installation. Remove check valve. Apply air pressure to check valve port "A". See Fig 1 . Air should flow from port "B". Apply air pressure to port "B". Air should not flow from port "A". If check valve does not operate as specified, replace check valve.