My general practice is to use the “pink” brush cleaner that the Martin F. Weber company manufacturers. It works beautifully. It’s pink and its called a Brush Cleanser and Conditioning Oil.
I pour a small amount of the pink solution into a foam paper plate or bowl and thoroughly work the solution into the brush hairs. You’ll literally see the paint lift itself right off the brush hairs and into the pink solution.
Do this until the entire pink solution is totally used up or very dirty. Rinse with clean odorless thinner and dry using a pinch/pull technique with a paper towel. You simply put a paper towel around the brush, pinch the bristles through the paper towel and pull the brush out of your fingers.
Repeat the cleansing process until the pink cleaning solution no longer removes paint from the brush.
Another technique: Audrey Golden from Florida reports that for older or more used brushes that no longer will retain that sharp chiseled edge we like, she’ll thoroughly wash the “bad” brush with pure Palmolive Dishwashing detergent that can remove oil and grime, using the same process. Once she has removed as much “dirt and ole paint” as she can, she’ll really load the brush up with the dishwashing detergent and pinch the brush badger bristles at the metal feral joint and pull out to form a chiseled edge. She’ll store the brush like that until ready to use. I’ve tried this with some success as well.