On Wednesday, September 2, 2020 at 11:00:06 AM UTC-4, John McLaughlin wrote:
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?

Yes, pneumatic switch can fail....first check is tubing (sometimes nipping 1/4" from tubes and reattach), maybe a switch clean/lube can fix the issue. Tube nipping is what I did in '70's/'80's US cars with emissions. Just a bit to get a better seal. My method is sorta cheap/easy....check again. Some sort of pressure/vacuum device gauge is more accurate. Yes, make sure it holds a value.....I remember a spring flight where "blowing on the probe" showed needle movement....long term showed the mouse holes in cockpit tubing.....good for me, I could fly wind noise, pitch attitude, "seat of the pants".. I did a couple hours local with no real instruments..