you dont want debris in your paint or clear so you shouldnt want it in your primer either. after all, if a chunk of dirt in your primer gets on the car....and you then spray paint and clear over top of that....you will still see it.
like was said,strain everything. I always mix my paint up into a clean mix cup,then from there strain into my gun. My gun also has a built in paint filter at the bottom of the cup. I also put an inline filter on my air feed to the gun to keep out any junk that may enter my paint. also a good idea to drain your compressor prior to painting to avoid any moisture in your paint.
not sure if you know any of that or not but its worth mentioning anyhow.