Here's my method
You need:
-Pure white industrial vinegar, no flavoring or any of that stuff
-Dirty Components
-Water (distilled and tap)
-Soap
-Toothbrush
For new components: I rarely clean out anything new unless I think there's some crap still in there. It's like washing a new car in my mind. If I think there is stuff in there, go to the next section.
For dirty stuff:
First, take the thing, be it a rad, res, block, whatever, and put it in a box full of vinegar. Totally 100% submerged. I leave it like that overnight, to loosen everything up so I can clean it much more effectively the next morning. I then dump everything out, rinse the stuff with distilled and see what comes out. For a radiator, I do a repeating vinegar/distilled cycle every hour or so until nothing comes out in the sink (a white sink helps a ton in this stage). For blocks, at this point I use the toothbrush in vinegar to scrub the channels and anything that might not be so nice about the block. After all the cleaning is done I usually do one final soak in the vinegar overnight and one big rinse with distilled water, then it's ready to use.
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