I always had the same problem as everyone here with Fiber and mixing it. Blenders created more of a mess, and stirring alone never un-clumped it properly.
Then one day I used my "aero-latte". And I am sure they have generic versions of them. It quickly withing 5 seconds blends it perfectly--and then 'down the hatch'.
A must have for fiber or cleanse users, imo.
Here is the link--but I am sure you can buy it almost anywhere.