Just flush the system with water from a garden hose. Connect one of the Prestone flush kits to the hose at the rear of the head and use a standard garden hose..........but........watch the pressure.

If you can open the block drain while you do this.........you're golden.

Finally, if you want to to the perfect job, remove the radiator and clean the fins with a commercial condenser cleaner and/or a pressure washer. The reward is worth this effort.