Nice! That's a great idea!

I have a few of them, as well as some other bottles that are the same material.

By the way - are "PP5" plastics able to be used? I'd need to double-check, but I'm pretty sure that's what it says on my Nalgene bottle.

Or must it say/be "HDPE2" instead?

I'm not seeing something about plastics in the Wiki FAQ, but I could totally just be glazing over it without notice.