Gdy wypijesz sok i butelka jest pusta, nie wyrzucaj jej.
When you drink 'a' (tutaj jest 'the' bo mowisz o czyms konkretnym) juice and the bottle is empty, please do not throw it away.
Mozna tez:
When you have finished drinking the juice.....
After you finished drinking the juice, and the bottle is empty, please do not throw it away.