I learned this from a Chinese man operating a stationary store (Chinese writing materials).  After using a brush, wash it out and while wet dip it in a dilute mix of musilage and water, slosh it around, the draw it to a point between the thumb and first two fingers of the left (or right) hand.  Musilage is no longer available so I now use Gum Arabic mixed with water.  I keep some ready mixed with my watercolor materials.  Gum Arabic can be bought from watercolor dealers.

The brushes dry stiff but easily loosen up in water.  Great way to protect them if you carry them out to paint.  Especially now with good days coming for plein air painting (without a camera Ha! Ha!)