I have a tunable Overtone whistle. I realize that the tube top tunable location has some kind of tape to let mouth piece and tube tightly fit. In other words, without this tape that the mouth and tube will be loose. Is this the typical design to tight the mouth piece with the tube for the tunable Overtone?
Yes, it is. It’s Teflon / PTFE tape, available in the plumbing section of any hardware store. It forms a good seal, and is very easy to replace if needed.
BTW, Overton(e) is a pretty good and descriptive typo!