See post 12 it's old but a good start
http://forums.vwvortex.com/showthread.php?3236636-Why-is-there-not-a-comprehensive-coolant-flush-DIY&p=42856729&viewfull=1#post42856729
http://forums.vwvortex.com/showthread.php?3236636-Why-is-there-not-a-comprehensive-coolant-flush-DIY&p=42856729&viewfull=1#post42856729