I've only got a small one!! ooh er missus. lol
I take the centre rod section out slowly, (otherwise it has a tendancy to come apart). Then empty and rinse the vessel. Refill with resin up to about 2-3 inches from the top. Finally, re-insert the rod in a twisting motion to ease it through the resin.
Make sure you give the thread on both vessel and cap a rinse before trying to screw together. Otherwise you'll struggle to get the thread all the way in creating potential leaks.
Hope this helps,
Lance