How to remove SS brazing flux ?

I have been using some SS/tooltip brazing flux which works fine for the item, the trouble is it forms a very tenacious glassy residue. I have been boiling it and a couple of hours seems to remove the flux residue fairly well but was wondering if anyone had ideas about additions such as acids or bases which might help it along. The glassy residue seems very tough and resistant to a chipping hammer, that just locally chips the surface. My sand blaster is currently not operational so thats not an option. Shame it isn''t like aluminium welding flux, go away for an hour and rinse off the remainder that pretty well dissolved itself.