I'm currently installing a solid fuel central heating boiler i.e. the plumbing is not for potable water. This is in Croatia where the only fittings for copper are end feed. I've been using up an old reel of leaded solder but have come to the end of that. I do have Fluxite flux (after trying inferior types of flux available locally). I don't really trust the lead free solder but are there any tips for getting the best results with it?