2. Pour about a tsp or so of shampoo on your brush and work in a good lather for another minute. Rinse it out completely, then add another tsp of shampoo.
3. After you work up a lather for the second time, don't rinse it out. Take your brush with the lather and set it in a small bowl. Add about a half a cup of hot water. Let that sit for 30 minutes to an hour.
4. Take your brush and rinse out all the shampoo under hot water. Spend the extra time to make sure you get all of the shampoo out so that your brush is squeaky clean. Shake your brush out, pat it down with a towel, reshape it to it's correct form, then hang to dry. (I hung mine with a magnet clip on my fridge.) Let it dry overnight. If it's still damp overnight, you can run through the ends with a hair dryer.
I've also heard massaging the ends with conditioner and letting that sit for a few minutes before rinsing out will keep your brushes soft :)
No need for expensive brush cleaners, regular shampoo works great!