I think Mitch is meaning to flush the fluid.
Mitch, just bleed as you normally would. Just keep doing it until you've got about 2/3 through the bottle of fluid.
That should be enough to have flushed the system.
Even better, use up a whole bottle from bleeding and topping up, then use the new bottle to do the final top up.
Probably overkill, but brake fluid's cheap anyway.
*awaits response from Dann saying I'm wrong
*
Dann,
This is not meant to offend in any way, I know you only try to help, so I am doing the same.
Often when you suggest somebody is wrong, what you actually mean is "there's a better/faster/easier way of doing it"
So unless of course the suggested method is wrong (in that it won't do what is being asked) perhaps try instead saying "There's another better way of doing that"
Again, I know you're trying to help people in an area you have knowledge in, I'm doing the same.
Part of my job is to explain to people why they're wrong, and generally they don't like it. So you need to choose words carefully.
Then once they're off the phone you call them a moron
edit:
so, turns out d!ckhead get's changed to hottie with the swear filter.