Uhhmm, something missing from that discussion on the "sludge/thickening" issue is the fact that most plastic tubing will leech resins into the coolant and that is where most of the "sludge" comes from.
You need to use tubing that is rated "food safe". It will leech tolerable amounts of resins into the coolant. If you can get a tubing that will carry alcohol and is food safe, even better. Alcohol is highly corrosive and will actually dissolve a number of polymers so any tubing rated to carry alcohol will do a very good job with keeping the water cleaner.
Just FYI.