Today, the glue had achieved its maximum endurance and the plastic layer seemed strongly attached. We didn't check it by pulling, just in case it could be removed by sheer force.
We assembled the whole prototype again (3rd version already) and put everything in their place. We forgot to cut the plastic sheet before gluing it. It is worth mentioning that we were also afraid it wouldn't hold together with a cut piece.
Anyway, we decided to use one of the cup hole as the entrance for the hose.
We have started to look for shops where we could buy all the material for the final structure and the Genuino sensors we need.
We'll keep you updated!