Hugh,
I use Vallejo Model Color paints but what I have come up with would work for Air as well. I clean my airbrush with the Vallejo airbrush cleaner. Mix it 50/50 with water as they recommend. It also works as a thinner. I've also tried a bunch of other formulas and concoctions from the interwebs; a myriad of chemicals in small amounts added to water such as glycol, glycerin, washer fluid, retarder, detergent, and/or alcohol. I never did get a formulation that I was 100% happy with. I abandon my efforts after I tried Liquitex Slow-Dri. It's not a miracle thinner, but it seemed the most forgiving for the way I paint.
Stuart