Second (third?) the Masters brush soap.
Use it after every session. Clean, rinse, then resoap. Let dry and cover tip.
Tip: Let dry point down so the dirty water does not get back into the ferrule. But do not let it rest on the bristles.
If they start getting really bad, I give them an overnight soak in this:
But put a clip on the brush so the hair is in the sause with the metal ferrule just touching the liquid. It will strip the chrome plading off of the ferrule, eat the numbers and brand off the handle and even take the black lacquer off the brush handle.
After the soak, pull across a clean paper towel and see the stuff come out.
Then go back to the masters and store.