Brush cleaning directions (step by step) are posted over the sink.
AND on our first quiz, I had a section where students had to put the steps
for cleaning a brush in order--and it was graded.
Also, like Deb, I've got a selection of awful brushes that were left over
from last year that students will use if I see that they're not caring for
the good brushes.
So far, though--between teaching them how to care for them and making them
realize that it's important enough to test them on--this has worked out