3-Port Check Valve
WARNING: This page is about a different car, the 1995 Mazda 929. However, it is still accessible from the selected car via links, so may be relevant.
Note direction of valve installation. Remove check valve. Cap port going to 2-way check valve. Connect a vacuum pump to lower port. Air should flow from port going to fuel tank with 3.0 in. Hg applied. Replace valve as necessary.
Courtesy of MAZDA MOTORS CORP.