I would be right there with you but the previous owner had everything done super early for some reason so I got a few more years. Service manual basically says to disconnect the radiator hoses, connect a flush gun and wash out the radiator. Disconnect the heater hoses and wash the core out with the flush gun at a lower PSI. Then with the engine isolated from both of the previous items hook up a flush gun and hose out the engine.
Here is a similar gun in operation: Flush Gun Video
That to me is a bit of overkill especially if your current coolant looks to still be in good shape and if you have lower mileage. I would just wait for a water pump failure or radiator failure to do the flushing gun stuff.
For normal maintenance I would just drain at the lower radiator, Refill with distilled, run to mix (few cycles of the engine fan), drain, refill with distilled, run to mix, drain a last time and fill with uncut dexcool. Option here could be to remove the thermostat to make the re-circulation faster but if you do that install a new thermostat and gasket.
Inspect the o-rings on the radiator cap. Replace if necessary.
Cooling system capacity is listed at 11.6 quarts so for 1 gallon of Dexcool into a cooling system with mostly distilled water left in it would give you about a 35/85 mixture. Dex-Cool is an ethylene glycol type of coolant. The main packagers of Dex-Cool specify no less than a 40/60 ratio of Dex-Cool/distilled, providing freeze point protection (FPP) to about -12ºF (-24.4ºC). All service manual says is to refill using 50/50 so 50% would be the target to shoot for.
That would mean after refilling and draining a few times what would be left in the engine would be mostly distilled water (maybe 90%??), lets just assume it is 100% distilled water left.
Adding 5 quarts of straight dexcool would get you a 43/57 mixture
Adding 6 quarts of straight dexcool would get you a 52/48 mixture
Depending on your location you can decide if you need the lower freezing point or the increased cooling capacity. In CA I would go for 5 quarts and fill my overflow with distilled.
More info here on ratios:
http://www.engineeringtoolbox.com/ethyl ... d_146.html
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Also on the overflow bottle. Not to easy to remove and clean out as you have to go in through the fender liner. Could just use a siphon ball with a hose attached to remove the majority of the fluid.