I use a different brush for each color (both applicator and buffing brushes). Never occurred to me that I had to clean them. Everything seems good after 2 years
I use a separate one for each color. They are actually foam applicators that I dab on a paper towel to remove any excess before putting them away. As for the buffing brush, you really shouldn't be getting that much polish on it.
Soak them in ammonia, was what a cobbler told me he did. He said it breaks down the wax, and the rest of the ingredients are tied to that. Never tried it, so YMMV.