I bought one of these... https://www.z1motorsports.com/z1-products/z1-motorsports/z1-motorsports-boost-leak-tester-p-1867.html?gclid=EAIaIQobChMI8frIoNWU6wIVB7zACh2w5wVwEAQYAiABEgJ9PPD_BwE
But you can make your own with some pvc pipe, and the appropriate gauge and fittings. Honestly, at 18 bucks the Z1 one is worth it. Your not gonna save much by the time you buy a gauge and other parts.