In message .uk, Ed
Sirett writes
Question is, do I need special fittings for this or will just fit a
normal 22mm compression stop-tap?
Can 1/4 turn ball valves be used in this position (more reliable?)

The pipe is more likely 20mm OD. UNless you measured it accurately in
which case I apologize.

Whatever you do any form of compression fitting on plastic pipe needs a
support insert in the end.



Dead on 22mm, measured with verniers. As the pipe was painted above
floor level, I had assumed it was copper until I pulled up the floor
boards and saw it was actually black plastic. A google revealed a couple
of threads suggesting this stuff is very thick walled, so I not sure it
does need an insert, or if a standard 22m olive will do the job.

--
steve