I have always had a problem with dry tip (or tip dry) with my airbrushing.  The Badger brushes I have owned have always been the worse.  Two nights ago it was the worse.  I barely got through shading my new snipers, techmarine and Lysander before it started.  I cleaned out the brush and moved on to dark green to work on some Kroot.  I got 5 done before it was unusable.  I cleaned the brush and put it in the ultrasonic cleaner and hit the interwebs prior to going to bed.

I found the video below.  


I actually tried what he suggested and I was able to highlight Lysander and the techmarine then finish 23 Kroot before having an issue.  The next day managed to do some more work and had even better success.  The one thing I change between a long painting session with one color.  I cleaned out the airbrush after it was empty which was about halfway through painting.  Took about two minutes but worked flawlessly.