When I flush my cooling system I follow this procedure:
Open the radiator drain, catch the antifreeze for recycling if needed.
Then I remove the radiator cap and put a garden hose in the filler neck with just enough water flowing to keep the radiator level up as the drain is draining.
Once youv'e got the flow right startup the engine (make sure you keep the water level up) and let it run until you see only clear liquid coming from the drain, shut the drain, the flushing is done.
Shut off the engine, let it cool down and then open the drain again and let as much water drain out as possible. Shut the drain again for the final time, I know this leaves some clean water in the system but what I do at this point is fill the system up with straight anti-freeze and start the engine again, heater on high and let it run, keeping an eye on the radiator level. keep topping off with straight anti freeze until the level stabilizes. Usually when Im done adding the straight anti-freeze to the clean water that remains in the system I end up with abvout a 50/50 mix when checked with an antifreeze tester.
I've been using this procedure for more than 30 years now on numerous vehicles i've owned and never had a problem.
You can get more involved and remove the drain plugs on the block etc, but if you follow regular suggested maintenance intervals for your cooling sysetm you shouldn't build up that much sediment in the cooling system.
I switched my vette over to the extended life anti-freeze, the orange stuff, and you can go up to 5 years before flushing. Only thing is that the extended life antifreeze will leak from places the green antifreeze wouldn't, a little tightening up on the hose clamps will take care of that problem though.
