Big Fat Lye Soap
I use this soap to clean all my brushes. It does a great job of cleaning out the paint and breaks down wax. Through the use of coconut oil, it keeps natural bristles strong and resilient by conditioning them as it cleans. Bristle is like your hair, and if you strip out all the oils with strong soaps, it becomes brittle and prone to breakage and loss. Big Fat Lye conditions your brush while it cleans without leaving behind a residue that can later transfer over to your project.
Pro tip: Rinse excess paint or wax from brush. Swish the brush around in the soap and work it through the bristles with your hands, then rinse again. You'll be amazed at how well this cleans your brushes!