Hello,

I was thinking about your descripton of the ink. Waterbased ink that 
dries into a waterproof crusty material sounds like acrylic paint. You 
may want to check with your supplier to see if this is the case. If so, 
there are products out that allow artists to remove dried acrylic paint 
from brushes with no damage to the brush. This same compound may clean 
your print heads without damaging them.

Have Fun,
Jeff