How to De-Clogg a cooling system of Doom?

[JohnSerbian]

Hi, so’s I have a 1983 GMC Sierra Classic 2500 that’s been sitting for over a year that I’m in the process of getting started. There’s a whole list of fun things that I gotta take care of first, but here’s what I’m working on now.
How does one de-clog a cooling system on a non-running engine? Flush the piss outta it with a flushing compound, cold, with a hose and maybe Lime-A-Way? Make my own Hot Tank solution out of caustic soda and dunk & boil the radiator for a day? The ‘Ol battery charger hooked up to a metal rod in a plastic container full of water and the radiator Shtick? Any thoughts? Mostly I just don’t want to pay a dime for any thing when doing it yourself is so much more of the way things should be done. Sometimes. That and I’m broke! Yes? No?

P.s.; I'll post picture's soon, Think: ''Brown Barnicals" & "Thermostat Clog"