The spring loaded metal washer backed rubber pressure relief valve is necessary for the tank to pressurize. The smaller disk valve keeps the fuel from just sloshing back and forth in the line when the primer is pushed. Of course the ball valve in the foot keeps fuel from draining out of the foot tube and back into the tank. They should be centered so they, including the ball in the foot, are free to move after the tank top is assembled. . . 🙂
