disc brake dust cover

I'm rebuilding my disc brake calipers and am having a heck of a time putting on the dust covers. Do you put in the piston in first then the dust cover or the dust cover first then the piston. whats the trick? Jim never mind put the dust boot in the caliper put the piston on the dust boot push down the piston with a piece of PVC pipe blow some air in the threaded hole and the dust boot blows up and around the piston magic Jim