So... a couple of questions...
a) Is this the original one, or the ebay-dud that you've resurrected? I presume you gave it a bit of a test before dismantling? After all, sellers have been known to tell the odd porkie, maybe the heating element is shot...?
b) That brass band (no, not the one playing in the bandstand, the one around the tank...), is that compressing the two halves of the tank together? I'm just wondering if, rather than Araldite, you could have used a high-temperature mastick/rubber-type seal instead, thus no worries about the Araldite giving up due to temperature. Of course, if the brass channel is just there to hold the glue in place, then fair enuff, glue it must be.
Anyway... until today I thought an "In-sink-erator" was one of those mincing machines, ala an American "Garbage disposal" unit, so you just lobbed any old stuff down the sink - meal left-overs, unwanted rats, children... - and it minced them up & sent them off to the sewage company for them to scratch their heads over...
I've used an over-sink boiler before now (Heatrae Sadia Streamline machines - very nice, but heavy on the juice), and my old workshop I fitted an over-sink handwash unit - not the "instant" ones (which are rubbish and consume more gigawatts of electricity than Doc Brown's time machine), but a tanked variety. Mind you, that ate a few gigawatts as well...