You can also do a search here; it's been discussed before. If you follow the proceedure defined in a Haynes manual (or the Ford repair shop manuals), it would not be nessesary to fill and drain the radiator to flush. Drain once, leave the plug removed, and continue to fill in the "overflow" tank until the draining fluid is clear.
"Never argue with an idiot; they'll only drag you down to their level, then beat you with experience"
2007 F150 STX Supercab (4.6 2V V8), Edge tuner, factory navigation, Mark VIII electric fan conversion with flex-o-lite controller.