Tipping when offered free drinks, I think so.
My wife and I visited a hotel where I know the owner. We sat for casual conversation with the owner for over an hour at the restaurant. He offered drinks. We kindly accepted. The server came by during our talk and happily brought us 2nds. We then went to the pool where the server brought us 3rds. My wife dropped her drink by accident, got a 4th. All free. Before we left, I asked the server to ring me up for a dollar so I can leave a $20.
That would be the right thing to do in this situation, right?