If you follow the actual flush procedure in the WSM it is quite labor intensive. I performed it once according to the WSM and have never done it again since. If it's a maintenance flush I will drain the primary system, fill with water, run, drain, repeat, then fill with 14L straight coolant and top up with water. If you get creative with the hose you can flush out the secondary system in a matter of 20 minutes. All said and done 2 hours.