If wanting to do a mega decent job also remove the block drain plug.
I simply use wynns cooling system flush for 200 miles or so prior to dropping water, it grabs all the crap and it forms as a congealed mush in the expansion tank, so needs clearing out, works amazingly well though, wynns say 10-15 mniutes but never had a problem my way, be aware though, if a sealing agebn has been used to seal a dicky rad or matrix this will remove the seal!!
tabetha