If you want to get a good flush without spending allot of money on the so called good stuff, just use a coupe of scoops of Electrosol Powder Electric Dishwashing soap. IT work great and is only about . 50 cents for your expense.
When I did mine, I wanted to use the Fleetguard 650,000 mile pre mix stuff. I drained down the system, removed the heater hose to the head and back flushed the head/motor and the heater core from that spot. I also had the thermostat removed. Once I got clear water, I reassembled everything, topped off and started up untill everything got warm and then put in the Ecectrosol. Went for a 40 mile drive and came back and drained down and rinsed as described before twice. Drained down one last time, used my compressor to blow out the heater core and radiator, installed a new thermostat after filling the block up to the thermostat housing with new Fleetguard, topped off the radiator and then went for another drive. Came back added 1 more quart and we were done.
The electrosol makes everything look new. The tip of using it was given to me by the Cummins Mechanics up at Cummins Northwest, said they use this method vise the $9/15 dollar bottle stuff and it works better anyway.