Closed loop extraction and vacuum pump

Hey I just setup a closed looped extractor and I filled the butane tank and got it to go into the work cylinder but not into the collection tank.
I didn’t vacuum purge the system
I’m wondering if that’s the difference causing the butane to not move on so to speak
Do I need to use a vacuum purge technique each time and how strong of a pump 3 or 6 cfm

You need to use the google machine
no offense but reading is fundamental
Merry xmas