As for beggers belief, unless you have tried first only then say so.
I suppose 35 years in the Sheet metal industry counts for nothing now....Oh well.
You do not solder kettles with soft solder or electrical solder, you use silver/hard solder or you braze them.
This is done using induction brazing/soldering, or in skilled hands, a fine oxy-acetylene torch.
What you are doing, is a bodge at best.
I suppose you have investigated the Toxicity of the soft solder you are using.