Block cleanliness

Soon I will have my block back from the machine shop after having it square decked, new cam bearings, also had one rod shortened.

Prior to final assembly I want to meticulously clean my water jackets and oil galleys.

I have a fashioned a sloped drip pan below the block on my engine stand (used a road sign) I have been finding large chunks of dislodgeed rust scale falling out of my water jackets when its upside down.

How do I get these large rust scales out of my water jackets? They are like small rocks. I dont want these in my motor....dont want heating problems or blockage either. I do have a pressure washer.

Would that hurt my block to use a gas powered washer to spray into the water jackets?

I plan to use dishwashing soap and bottle brushes to clean all my oil galleys and crank prior to assembly as recommended by one of our members.

Thank you.