So, when you get around to it, we recommend using unscented baby shampoo to scrub your brushes. Once you’ve finished getting all the makeup residue out, be sure to dry the brushes upside down with a clip.
If you have a can of Coca-Cola in your fridge, just crack it open, pour it over the stains, and leave it overnight. The carbonic acid will break up the stains, and then you can finish washing them away with a bucket of hot water.