Cleaning the inside of soldered copper

So I soldered up my recirc tube for my immersion chiller, but before I use it, I want to clean it well enough - any suggestions on that??  PBW bath or something different first?

I think I’d just use boiling water to remove any leftover flux, then the first batch will quickly passivate the metal.

Maybe I’ll try a couple separate batches of boiling water for good measure!