Best way to test as its vacuum side? Do the leak test with a compressor and see if air leaks?

using the Perth-WRX mobile app

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2002 WRX (GDA) BUGEYE, 204BHP at 290Nm, daily driven

--MODS--
--> Walbro 255LPH fuel pump
--> Grimmspeed 3 port EBCS
--> 3" turbo back exhaust
--> Catless up pipe