You can actually flush the system without that kit.
Do the following on a cold engine:
1.) Drain the coolant into a suitable container using the pet **** on the driver'* side bottom of the radiator.
2.) Leave the pet **** closed
3.) Fill the radiator with regular water from the garden hose.
4.) Start the car. Let the water circulate.
5.) Open the petcock. See the coolant/water combo.
6.) Repeat that process a couple times until you get nothing but clear water out of the petcock.
If you feel inclined to do so, you can put water through either of the heater core lines that come into the engine bay. Just don't use pressure. Regular water pressure will suffice. You can also back flush the water pump by removing the lower radiator hose. And, if you want to backflush the LIM, remove the thermostat and run water through the LIM.
This is how I do it. Doing all of this makes me feel confident that it'* been done as well as can be. AND, I saved a few bucks on the cheesy Prestone flush kit. Little messier, but worth it, in my opinion.
Oh ya, don't refill it with Dexcool. Use the Prestone "mix with any color" coolant.