I will have to take my chances on being shot down, but I simply have not had the time to go back over so many posts.
Just wondering if any consideration has been made on how icicles form?
Water from the pitot drain would I suspect be only just above freezing, so meeting 800k/hour sub zero air on the outside would probably induce a further blockage in the form of a lump of ice externally.
Maybe the pitot needs an external heater also?