Chris Hogg wrote in
:

I have in the past 'welded' the crack from the outside with a
soldering iron, but included in the weld a bit of stainless steel mesh
to provide reinforcement. I trimmed small pieces of plastic off the
inner rim of the butt to provide extra material and act as a welding
rod. On the inside, I applied some black Unibond gutter sealing goo
(after the butt has been well dried). Water pressure will push the goo
further into the crack, assisting the seal. That was several years ago
and the repair is still good, although I see another crack is
appearing nearby (both are near the tap; obviously a point of stress).
Be aware when using a soldering iron that the plastic melts very
easily, and it's quite easy to make a narrow crack into a great big
hole.

Thanks, Chriss; just the kind of guidance I needed! Where did you get the
stainless mesh from?

Al