and close some sort of a valve to let it sit in order to see if it holds the vacuum. You'll never pull a large enough vacuum in the small volume of the gauge. You might be able to see the needle move but that about all. You will need to screw the gauge into something like a foot long by three inch section of PVC pipe with end caps. Have a 1/4 valve screwed into it as well. Pull the vacuum on the pipe section which will also pull a vacuum on the gauge, close the valve and let it sit. If you loose the vacuum then you have a leak in the gauge. That's assuming you glued the end caps well and tapped for the fittings correctly. If you have an electric air pump that you can plumb backwards so that it's sucking the air out of the intake it will probably pull a deep enough vacuum. A "water Puppy" would probably work as well. You would be running it dry but not for very long. That's a couple of hours on an afternoon for you. Good luck.