Others may correct me, but I understand Future to be the same as a clear acrylic paint that you would buy as such. I have sprayed Testors acrylics (although not yet their clear acrylic ) and cleaned up with their Aztek Airbrush Cleaner. I would think that would be appropriate for Future as well that is.
Tester's site is at http://www.testors.com/Default.asp Do a search for "cleaner" and you will see it. I have bought it at my local hobby shop.
I'm sure there are other optiions which someone may point out.