I haven't resorted to duck tape, but I also wake up with mouth very dry. I had my 2nd sleep study last Sunday night, so I'm back on the CPAP again after 3 weeks off (per my dr recommendation). Until the DME people can 'tweak' it, I'm still at a pressure of 10 and still waking up as sleepy as when I went to bed. Hoping for some kind of relief.........
It's nice to know that I'm not the only one with this problem, but it would be nicer to know of a solution to the problem........

jpino, What is your new pressure requirements and what type of mask are you using?  If you're using a nasal mask of some sort and having dry mouth problems it's likely you are opening your mouth in your sleep and this will render your treatment ineffective.  If you're using a full face mask then you may want to increase the humidity some (assuming you have a humidifier).

I have the nasal pillows with a heated humidifier. The last sleep study tech said she had to turn the pressure up to 17. I don't have the printed report back, though, so my machine at home is still set at 10. I did 2 sleep studies with the pillows and neither of the techs mentioned me sleeping with my mouth open. I can tell at home if I open my mouth (to yawn or cough, etc) that the air kind of rattles around. I can't imagaine that I could sleep like that and not notice it and my mouth is always closed when I wake up.

A dry mouth is an indicator of sleeping with your mouth open because all of the air rushes out of your mouth.  You could try a chin strap too instead of going with a full face mask.  If you're sleeping with your mouth open and air is leaking out of your mouth, your treatment won't be effective.