Originally Posted by 1fastbmw
It seems a vacuum pump is the only real way to do it without removing the whole unit to get the back cover off. I do not know if it is a good idea to fill with a little part thiner / brake clean after you suck out what you can to loosen any stuff on the bottom and then suck that out.
My advice is anecdotal, but it would seem that any brake cleaner or thinner that you left behind would be worse than not getting the last residue of old fluid out.
Great thread. Kudos on tackling this job yourself.