I'm tackling a slight, but long-term leak around the base of our
back-to-wall toilet (one of this sort of thing:
http://www.bathstore.com/products/toilets/back-to-wall-toilets. It
has a boxed-in, concealed cistern (like this, but an unknown model):
http://www.screwfix.com/p/fluidmaster-concealed-cistern/30168; and
I've traced the problem to the point where the 90-deg flushpipe enters
the back of the toilet, within the boxing.

Problem is evidently that the installer cut the flushpipe too short, and
has extended it with a nasty bodge that isn't working well, and it's
leaking. I want to either replace the flushpipe (preferably) or extend
it properly. However, this pipe seems to be an odd size, and I'm
struggling - it looks like 38mm OD, as opposed to 32 or 40mm for
conventional waste pipe?

Any ideas how to proceed? I can see that (eg) Screwfix flog a new
flushpipe; but God knows what size that is and whether it will fit my
unnamed cistern: http://tinyurl.com/ljfeps6 (or
http://www.screwfix.com/p/fluidmaster-flush-pipe-16-x-14/53204).
There must be an alternative to possibly fitting a whole new cistern!

--
David