In my experience you have a couple of options. A few washes with dish soap and oil will work, but, your bristles are going to splay out. The second is a brush cleaner and conditioner. I buy that at Home Depot. Let the brushes soak until you can get all of the paint residue out. May take an overnight soak. Either way, management of the bristles while drying is important. Wrap them in a paper towel, a sheet of paper, or slip them into a baby sock to keep the bristles in check.