Fittings in good condition are eminently reusabe. Just pull apart and, when
reusing them, clean the excess solder out with a quick heat and a slap on
something to remove the excess solder so that you can fit the pieces back
together.
As to the "Tinning flux", it is merely a flux which you can spread easily
over the copper rather than something that puts solder on the copper. There
is flux that has solder chips included in it if you want to go that way with
a one-step tinning solution but the flux and solder isn't cheap.

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Why isn't there an Ozone Hole at the NORTH Pole?