The day I had "clean brushes" on my to-do list, I happened to find this gem of a tip in Self Magazine. I absolutely love it. It's easy and my brushes are cleaner than ever!
To Clean & Disinfect Makeup Brushes:
1 cup of water
1/2 tsp of tea tree oil
and a dollop of baby shampoo.
Swirl your brush in the mixture, rinse, re-shape and let dry.