okay, so shampoo it up, and leave it stuffed with lather for a good while... sounds good.
I used to paint warhammer models, and the one thing I learned about brushes was to never store them wet in any way but on their side, or bristles facing down... it makes the hairs fall out and get messed up if they are stores bristles up.
Does the same go for a shave brush? I would imagine but perhaps they are more resilient.