I had always been very diligent every time I used wax resist to quickly scrub out the resist. This kind of worked to make a brush flat last a bit longer, but slowly wax was building up in it. The other day I forgot to wash out the brush at all, a trashed brush, I thought. I found a quick way to make it come perfectly clean again. I took a small glass jar and put a little water and dish soap in the bottom. I stuck the brush in it and put it in the microwave for about 10 seconds, until the water was slightly boiling. I pull it out of the microwave, swished around in the solution. The brush was absolutely clean, like brand-new, no wax.
I thought others might find this discovery useful.