flushing 350 block

This week I'm finally getting around to flushing the 350 block in my 56 belair. This is in an effort to find out why it's heating up like crazy at an idle. Since the radiator is new I would like to limit my work to just flushing the block. I've located the block plugs on each side now where do I go from here? Do I simply attach a garden hose to the inlet on the intake manifold and let it rip? What if there is so much crud in the water jackets that ordinary water pressure doesn't penetrate it? What are my options then? Should the motor be running when I flush? Any help is much appreciated. Thanks. B Chase

One or two really good flushing jobs should be plenty. If it still overheats, I'd look at other areas for the reason.

Overheating at idle is either fan clutch if so equipped or the water pump.

If it is heating up only at idle and not under power, it's probably an air flow problem and not a water flow problem. Are you still running the original 2-core radiator, no shroud, and 4-blade fan? AC? I've replaced my original radiator with a 'Desert Cooler' 4-core one, added a shroud, and have a 6-blade fan on my '55 Chevy wagon w/ a 350/700R4 setup. No problems idling or under 'normal' conditions, but I still had a heating problem crossing the Mojave desert last summer at 65mph, so I'm going to put in a new thermostat and try Redline Water Wetter before resorting to a new water pump.