have been doing the bathroom and a neighbour (a plumber) recommended
using grey plastic pipes with screw on connections, which include 4
different 'rings' that must be put on the correct order. a black
rubber washer, a metal grab ring, a white plastic thing with thread on
it (like ptfe tape) and a plastic grey ring.

then tighten it all up. however on two of these elbow bends, i've had
the unfortunate experience of the pipe 'popping' off the connector. as
all the plumbing is boxed in behind tiles i'm worried about it now.
so i wonder if anyone here knows about these connections and if they
are really better than plastic white push fit which i understand and
havent had any problems with??