Any suggestions on cleaning these coolant passages full of rust and stop leak products?

I was considering pulling the block drain plug and using compressed air to push the mess up out the top of the block if possible.

Ideas?

 

Pressure washer?

I don't see compressed air working too effectively.

 

Yeah it's in my garage though, I guess I could roll it out

 

I hate to say this but really the best way is to have the block hot tanked!!

Red Neck Hot tank is metal drum large enough to hold the block with a wood fire underneath

 

I have been hearing some great things about Evaporust but have never tried it. I wonder if filling it with something like that and letting it soak and then pressure wash it out would help.