I have a method that I consider to be a poor boy flush. I drain the coolant from the rad. I close the drain valve (or in a newer car, put the lower rad hose back on). I fill the rad with distilled water (it's cheap). I then take it for a ride and turn the heater on until the engine is at operating temp and the heater is blowing hot. I go home, have a beer and let it cool off. I then drain the rad again. Now, if I feel like it, I dump in distilled water again and repeat. When I drain the rad for the third time it's pretty clear. I then put in the full strength coolant equal to about 60% of the system and top off with distilled water. I then take it for another ride to get rig of any air bubbles and touch up the tank with 50/50. I have on hand a few extra empty jugs to store the the coolant from the three times I drained the radiator. I dispose of the fluid at the local recycle place. I never bother with the block drains and I don't bother with a flush compound but I guess I could. Done for 5 years. My oldest car has 17 years on it, and has had 3 poor boy flushes like this. Still on the original radiator and water pump.