In message ,
Tricky Dicky writes
If as you say it goes into a cast iron pipe and you cannot see any
fittings on the pipe then I would suggest the pipe is lead.

Forgive me, perhaps I'm an idle sod or a bodger, but I think many people
are over thinking this. Given that the pipe is out of sight and only
occasionally emits pongy air, not gas or liquid or anything under
pressure, I would just cut a circle of thick card or plastic and attach
to the front with a few crosses of gaffer tape. Who is going to see it,
or care? Should it fail after ten years, just renew for the next ten
years. And yes, I have done exactly that, in the past. Job done.

--
Graeme