A good back flush uses air pressure as well as water. Adapt a garden hose to the lower radiator hose, with a small piece of fuel hose teed into the adapter. I use a piece of exhaust pipe with a 3/8" copper tube soldered into the side.

IMPORTANT! Extend the top radiator hose away from the engine compartment so you don't flood yourself and everything under the hood. Fill the radiator from the bottom with the garden hose and then goose a quick shot of air pressure into the small pipe. The shock effect of the air will dislodge debris in the radiator and flush it out the top hose. Refill and repeat several times.

Cleaning out the block is almost always a manual job with a probe through the freeze plug holes. Using a pressure washer wand to flush out the dislodged crud is a good idea, but it's usually necessary to start the process by digging at the accumulated crud.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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