I was always told just make sure to use the red power steering fluid.. its what I use with no problems (well, the truck steers too easy, if you call that a problem)
But ya, take off the return line, turn on the truck, and keep filling up the res. with ATF, trying not to run the system dry. Then I would put the line back on, flush the system by turning the tires back and forth, then drain and re-fill again.
But thats just how I would do it.