You need a " Kuhlman Gauge " Kuhlman is a brand but is used like Band Aid , Jello. Compressed air is fine, these gauges have a hand pump / bicycle pump.

It is a chamber ( Manometer ) with liquid that will bubble if pressure in the line drops. The test takes 5 minutes or so, not like pumping things up then waiting overnight.

Do a search and someone will have a vid / animation of how it works.