Having disturbed the plumbing, I have a pitot leak! Being a turbo, the
glider has a pneumatic switch to select between nose and tail pitot
tubes. With nose selected, there's a leak. With tail selected, things are
much worse and I can't measure any pressure at all from the tail pitot
tube.

So should I suspect the switch or the connections to the switch? And is
it possible for the switch to have an internal fault which could cause
these symptoms?