I dont store pollen long term since I kept my breeding moving a generation forward.
What I do is collect the sacs as soon as I notice the tip slightly opening. Place them in a letter envelope and store it in a dark for 2-3 days. Around that time the sacs are dry and all I do is tap the envelope for the pollen to drop. I end up with more pollen than I need.
I used to do this with plastic/glass vial but a lot of time the pollen ends up like a cake because the moisture from the sacs cant escape. Since using the letter envelope, my pollen have never caked up and remained dusty.