I use toothpaste for fittings, inside of blocks, works very well for fins, just make sure you pick up toothbrush that is hard or extra hard, you wanna get between those tight fins and get gunk out or remove stain, if you had color in your fluid. For rads, I use just hot tap water and let it run through em, I had mayhems blood red stain two of my rads pretty badly inside, the fittings and o-rings needed good wash, treads were bad as well, walls of rads were affected by color change but nothing major, for that thing to wash out, you would need some type of cleaner like blitz kit I guess, however I didnt bother with that, I washed em with hot tap water out and afterwards, I used just clear coolant, the stained rads didnt affect color of new coolant and there was no undesirable effects on new luube as well, however some part of my rads inside are still a bit red, thats why no more colors for me, I want clean rads inside. I use toothpaste for everything except rads.Sorry if I've missed something but what is recommended to use to clean the loop components, radiators and system as a whole? Would a cycle of dish soap work? I'll actually be putting a brand new LGA 1700 CPU block in so the only existing components will be my GPU water block and pump/res. I know Mayhems Blitz is trusted but it's far too expensive to order from the UK these days.
If you want something to clean your system without you needing to disassembly it, I have no idea, better clean everything properly and change tubing too.