There are three thirsty customers in the bar. You could serve them some swill. Collect the empty tankards and give them what they want.
This is the low-spoiler guide for "Serve the swills" puzzle in Goodbye Deponia. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.