Tina: actually "comb" with another hair brush!
Make a mixture of baking soda & hot water (I use an old cup) & put brush in & let sit for 30 minutes to 1 hr. Rinse with hot water & air dry.
My mom would fill bathroom sink with hot water and ammonia. Let sit for an hour.
Rinse. Use comb to remove the hair and dry.
I was a stylist all my adult life. Using a shoe box size Rubbermaid container or any one that is long enough for a hair brush, using hot water and Ammonia as Sandie60 said. Use enough water to almost cover the brushes then add enough Ammonia to cover all. I add all my combs to this also. Keep it covered and let them soak, I do this all the time and have a container always ready for combs and brushes.