Have you driven the car and/or pumped the brakes (since adding the PS fluid)?
If not, get as much of the mix as you can out of the master cylinder before you do any bleeding. You'll be better off pulling the stuff out through the top of the system than flushing it all the way through. Once you've emptied the BF reservoir, refill it (with BF this time of course!) and bleed the whole system. Repeate at least once.
FWIW, if you can find a BF that's the same type (DOT4, DOT5 etc), but a different colour than your current fluid mix, it'll be easier to tell when you've got all of the old stuff out. A vacuum pump (
Vacuum Pump at CT ), if you've got one, would be just the ticket.
Haunz is right about the possible outcome - don't delay in getting something done about it.
Good luck!
Cheers,
--
Terry McG