Hi everyone, as promised I have returned to let you all know how I got on, but I found the original thread “locked”, so here is the “update”.
The holiday was excellent and accommodation first class, out and about every day and entertainment every night, and most importantly no flying “accidents”.
Let me explain, a few weeks ago I was watching a movie at home and did not realize that the leg bag had become full. When I stood up, and gravity takes over, the extra rush of water was enough to pressurize everything and the adhesive catheter “blew off”, fortunately this happened at home so I did not have the embarrassment of wetting myself in public.
Hence my concern that when the plane gets to cruising height and the cabin pressure decreases, would the adhesive catheter “blow off” if the leg bag became pressurized. As a result of some good advice, I realized that its air that expands not water, so when the leg bag starts to collect water, instead of opening the valve in the usual manner to empty the bag, I turned the bag upside down and gently opened the valve to purge the residue air out of the bag and most of the water and then closed the valve not allowing any air to re-enter the bag. I tried this out for a few days before traveling to make sure of the logistics, and I did this immediately prior to boarding the plane. Thankfully I did not experience anything pressurizing and to make sure I checked everything out once the seat belt light went off.
Another experience and another hurdle overcome, although I admit I may have amplified the problem in my mind. I don’t know if things would have been ok had I not done any preparation, but evacuating the air out of the bag was easy to do and gave me reassurance that the catheter would not blow off.
Thank you to everyone who took the time to respond to my request for advice and I send my best wishes to you all.