A boiling kettle is essentially a large pot – big enough to hold 40-50L of boiling liquid. New a pot of this size can be quite expensive, but if you’re lucky there are a few alternatives.
Trawling the op-shop may turn up a large stock pot or an ex-commercial kitchen supplier might have such a thing on the cheap. The other option is to convert a keg – although it isn’t easy to find kegs being retired from service. I was lucky enough to do just that.
With a quick nip and tuck with an angle grinder it makes a very serviceable pot. It does take a fair bit of filing to get rid of all the burrs!
To avoid the need for any tipping or syphoning I have elected to fit mine with a tap, so that once the boil is complete the liquid can be drained straight out.

The photo below shows the flanged backnut and washer used to seal the threaded pipe into the wall of the keg. The washer I cut with a scalpel out of a cheap dollar-shop silicone muffin tray by using a backnut as a form. It should be good for 300C so, fingers crossed, no leaks!

The 20mm hole required was a bit of a challenge – my largest drill bit is 12.7mm. Ideally you’d use a bimetal hole saw, but I refuse to pay $30 to $50 for a single hole. So in the end I simply enlarged the hole by hand with a circular file. Sounds like a terrible job, but it didn’t actually take that long.
What isn’t pictured above is the copper extension that goes on the inside of the keg to draw the liquid from the side of the keg rather than the middle where all the sediment is. Perhaps a photo of that in the future…
Spend for my kettle: $25.
Retail pot: $200.
Spend so far: $155.
Savings so far: $1540.