If you open the air line and fuel shoots out, you tank isn't plumbed correctly! The check valve should be in the line that goes from the pressure side of the pump to the top of the tank. It is there to prevent pressure from leaking back into the engine. Make sure that the pressure line (with the check valve) goes to the highest part of the tank. When you remove the line to bleed the pressure off, pinch the line between the tank and check valve. Then remove the line from the tank side of the check valve and slowly release the pinch on the line.