"And don't be surprised to find green, yellow, sticky, grey crud in the housing."

This is just why you should take this opportunity to drain the coolant out (drain valve at right rear lower side of engine. The coolant is anti-corrosion for the whole cooling system and heater core and lubricant for coolant pump, and these characteristics only last a couple of years. Flush water through engine block coolant channels when drain is open, but don´t run engine with water only in there, since then the pump gets no lubrication.

If you want to clean out thoroughly, run with new coolant for a a couple of days and then drain again, and replace a second time with new coolant. Always use 50/50 blend with water.

Gustafkalle