Hi

Before I go mad I'd like some suggestions on how best to fix my weeping
shower couplings.

Some background: I'm in the process of completely re-fitting my
en-suite, and I'm installing a Grohe Rapido-T concealed shower mixer
(35500) which will feed a fixed rainshower head and a hand shower.
Before I board and tile out the wall I wanted to pressure test my
plumbing to make sure it is OK (no going back afterwards).

The problem is that, no matter how hard I tighten up the 1/2" to 15mm
coupler feeding the outlets one of them still weeps when I force the
outlet to be closed. I know in practice that the outlets will always be
open so there will be no pressure on this connection, but I don't think
that is the point (unless I am wrong?).

The weeping is coming from under the coupler where it touches the mixer
socket. The socket body of the mixer is so deep as to mean the bottom
face of the coupler doesn't come up against any face so I can't use a
fiber washer. I've tried plenty of ptfe to no avail.

One thing grohe have used is a rubber ring on the sealing plug which I
have removed to fit the coupler. Is this the way to go? If it is I can't
see anything suitable in either the screwfix or toolstation catalogues.

Any other pointers before I pay somebody with more experience than I to
fix my problem?

Shower photos:
https://picasaweb.google.com/kev.hol...eat=directlink

(http://bit.ly/IdKQvz if the above wrap is broken)

Coupling I'm using:
http://www.screwfix.com/p/male-coupl...equestid=86095

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for valid email reverse liamtoh