" I don't have the oxy acetylene kit and brazing is a bit of a dying art in Ireland. Perhaps there is another way to attach the outlet?"
You can use a bulkhead fitting. Google brass bulkhead fitting or stainless steel bulkhead fitting. Get them with fuel resistant O rings. If you can't reach into the jerry can to install one, thread a bit of string into the filler opening, and out of the hole you have drilled into the bottom of the tank. Slide the male part of the bulkhead fitting down the string, etc.
I use them. They work great. Not expensive, easy to install
Cheers,
Hugh