easiest way is to remove a heater connection pipe - connect a fresh water garden hose to it, let the water flush out everything - keep radiator drain open, close the drain, remove your setup, rinse and drain with distilled water once and fill up half quantity of coolant concentrate in engine and top up with distilled water till it burps no more.
Done it thousands of times.
If you are concerned with tap water then find a 20 litre bucket, fill it up with distilled water, make a pipe nipple fitting on the bottom of bucket and use it at elevated height to allow the distilled water to push itself through the engine from heater connection pipes as flush medium and out the drain tap of radiator.
You can also use a fountain pump for this purpose. Even an inverter coolant pump from a Prius works nice for this.
