The Masters Brush Cleaner is my go-to brush soap. You can also use rubbing alcohol (it works insanely well), but it will strip the oils out of natural hair brushes. To prevent drying, rinse the brush well and wash with brush soap. If you want to go crazy, use an ultrasonic cleaner with just water, diluted Simple Green, or even alcohol. Regardless of what you use, I suggest that as a final step you leave a bit of soap on the brush (too much is okay). Shape the bristles into a point and let it dry. The bristles will get rock hard, preserving the tip and preventing damage. When you want to use the brush again, just swirl it around in some water to dissolve the soap.