Hi, DeHe--

Elder DS used to be a big chewer.

I'd probably give up the spout and move him to a metal water bottle, but then be prepared for the behavior to emerge another way, whack-a-mole style.

Some people feel that increasing sensory input in other ways helps (joint compressions, trampoline, chewing gum, etc.).

You might ask him why he does it-- doubtful at his age that he'd have insight as to why, but you never know...

DeeDee