I rarely used to prime them at all. I would transfer the beer to the pin when it was ready, usually from a secondary fermenter, and dispense by gravity...simply pour the beer through the tap and allow the pin to collapse as it empties.
I never left beer in the pin for a few weeks before it was...
I have been using them for over 30 years......used to get them from the off licence in the UK where they were used for bulk sherry.
I used them to serve ale by gravity...They will collapse as you draw the ale. You can push on the top of the cube to make sure no air enters....Best for a party...