When I spray acrylics I use a product called Airbrush Cleaner (can't get more generic than that) made by EZ Air... it is a soap based solvent with Calcium Carbonate in it. This stuff cleans the exterior as well as the interior of airbrushes, it's a lot like soap. And it's enviromentally friendly.
I wash out my bottle with water, make sure no paint residue is inside, then put about a 1:4 ratio of this cleaner to water. Spray it through my brush until clear, then remove the nozzle and let it soak overnight in the same bottle (if I am done) to remove the external coat from the tip.
you can get it at Michaels or Hobby Lobby... I think it only cost about $1.50 or so and I've been using it about 3 months without having to buy another.
For tough jobs I spray 91% isopropol then put the nozzle in the same said cleaner...
I like it because I can get any overspray off my skin with it etc a lot easier than soap and water... it also is good at dissolving dried acrylic...
the only warning is against prolonged exposure to skin.... the calcum carbnate will dry it out skin and irritate it if applied and allowed to sit without washing...