This is the procedure I use. It is done on a cold engine.

1. Drain fluid. Open radiator petcock and engine block plugs.
2. Remove the thermostat
3. Reinstall the t-stat housing and upper radiator hose
4. Disconnect upper radiator hose at radiator
5. Flush system with garden hose through upper radiator hose until water runs clear
6. Disconnect heater hoses, open heat valve
7. Flush heater core
8. Flush overflow tank
9. Drain as much water as possible from cooling system
10. Siphon water from overflow tank
11. Reinstall thermostat
12. Button everything back up
13. Refill cooling system with specified amount of antifreeze, bring up to level with water, preferably distilled
14. Run car, top off coolant
15. Keep adding water as required every morning until system is topped off.

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95 E320 Cabriolet, 169K