Ooooh, I have to Interact while holding it, haven't tried this, I was just dragging and releasing the bottles to try solutions. I guess the way it is now it's less intuitive. It didn't cross my mind to try this. Nice ending, btw!
And don't feel bad about this, it's just a bit unclear. In my game, no one even realises that there's some bigger objective! Lessons learnt, we just became better at game design!