removing flux residue

[Petal]

I've always used Alum pickle and if it doesn't remove the residue, just leave the piece in for longer and add some more alum crystals to the water. I hardly use Auflux any more, as I find the solder doesn't run all the way through the piece, whereas it does with borax.

[Dennis]

All these different opinions are the whole point of the forum of course.
Auflux has been my go to, even for large pieces like belt buckles, but it does get exhausted more quickly than borax. So it will not allow extended periods of heating.
Safety pickle in a lidded slow cooker does not give off any noticeable fumes, nor do nearby tools get rusty, or corroded.
Dennis.