Tried and tested, here's my go to for this DIY.
1/4 cup Witch hazel
1 tsp Castille soap
1/2 cup Distilled Water (or Boiled water)
1/2 tsp Coconut Oil or olive oil
Empty Spray Bottle
Combine all of these ingredients together and place into your empty spray bottle.
How to use:
1. Shake the ingredients in the bottle
2. Place your dirty brush on a small hand towel you don't mind getting dirty.
3. Spray your dirty brushes with your mixture where the bristles are on the towel.
4. Rub the brush on the towel in a circular motion and you will see the product come right off your brush.
5. Lay flat to dry on the towel.
** One additional step I started doing this year was disinfecting the handles of my brushes. Take a paper towel and dab with a bit of rubbing alcohol and wipe the handles of your brushes clean. You'll be amazing to see how much makeup and dirt come off.