Bob, my guess would be get it all.....even if you have to fill it with pink and run your pump to thin out the water, drain then refill. maybe twice.
Keep in mind, pink stuff is cheap, so wasting a little won't hurt. And to avoid all this work next year....just run it year round.
This subject came up on DDR too , you might give it a read too.
http://drr.infopop.cc/eve/forums/a/t...2/m/7727026095
Rick