Dependant on elevation....you can get the adaptors at any auto parts store both screwed and the quick connect type.
Also very important to pull that vacuum , if it wont pull down to 30 inch vacuum ,on the gage negative,
you have a leak . Check all your gage connections first. I know you guys dont have nitrogen but leak checking with a nitrogen charge will also dry out the system. I do a triple EVAC and break with dry nitrogen ,cheaper then using ref. 12 or 134A to leak test. Note make sure the gage is zeroed out set screw in the face.
Most AC leaks are compressor seals. I tell my buddies all the time use it or loose it. Using the AC keeps the seals wet with oil.
Did you add Freon?