Chieftain tuning question

Santa bought me a new tunable Chieftain whistle, which I’m enjoying. I have a question about the tuning, though. The friction of the tuning slide is so light that the length shortens as I play, and I gradually get out of tune after playing several tunes. I tend to play with a heavy hand, so maybe a lighter touch would solve the problem, but I was wondering if there were other solutions. I’ve considered duct tape to keep it in place, but I’m hopeful someone has a more elegant solution.

The slide should be quite tight,if it is loose please send back to the retailer who will send it back to me or send to me direct to save time.KWL 20b Blackwell drive Watford Herts.UK.I’ll have it fixed and back return of post.
Sorry for any inconvenience.
All the best
Phil.