Go to Becky's bar, on the other side of town. Go down the stairs and use a crowbar on the still. Go back to Frankie and receive the reward.
Once you've completed this quest, Becky won't talk to you anymore, so make sure you've done all of her quests before completing this one.
Or tell Frankie to buy his inventory from Becky, you will gain more experience and no Karma loss.