I just flushed the system with Peak radiator flush and added new Prestone Premixed Dex-Cool antifreeze. It took about 1.25 gallons of premixed antifreeze. I plan to flush the system every 5 or 6 years and replace the antifreeze every 2 to 3.

Steps were as follows:

I removed the thermostat. It’s your choice on whether to do that. With it removed the engine won’t heat up much during the flush, but you won’t have to wait for it to reach operating temperature and open the thermo on each of these steps.

Drain the antifreeze from the system at the 2 drain fittings. The heat exchanger drain fitting is toward the back of the heat exchanger on the port side (there is a fresh water drain there too). The other antifreeze drain fitting is toward the middle of the engine block on the stbd side. I drained them into the