what paint are you using fist of all?
if water id use warm water and these
http://cgi.ebay.co.uk/5-PCE-TATTOO-T...item335ac7b786 same as with non water based just use thinners remove the nozzle and draw back the needle and give them a good rooting with the brushes repeat if needed then when you spray a cap of water through place your finger over the tip of your brush so it bubbles back into the bowl see if any paint is remaining if there is repeat the process with the brush again till clear
hope this helps a little
edit; forgot to say good work on your shell mate keep up the good work