ASME A112.1.3 pdf download AIR GAP FITTINGS FOR USE WITH PLUMBING FIXTURES, APPLIANCES, AND APPURTENANCES 5.1.2 Lower the water level so that it is no more than 0.12 in. (3 mm) below the highest level of air port opening, and apply a continuing vacuum of at least 25 in. Hg (85 kPa) while the water level is gradually lowered further....