Is that coolant system flush in a bottle stuff really necessary..has it ever done any damage?
I just disconnected a hose near the thermostat (4age though) and fed water through there (with heater control in cabin set to full hot). After that I also filled up the car with plain water, ran it with radiator cap off until warm, drained that out and then filled up with coolant and water. Remmber to bleed system which basically means leave radiator cap off from when the engine is cold till when it heats up (while idling), see bubbles come out at top of radiator. Some guys her told me to park car on uphill so the radiator cap point is highest so air will be bled out easier...had already finsished before that though but sure it would be good
EDIT:
Listen to Les below - the cool guy in sunnies, ensure the motor has cooled down quite a bit before you refill the system