Old bloke in the bar, tells tall tales of his adventurous past to tourists and passing trade, in return they usually buy him a drink. If the are not quick in providing the tipple, the storyteller leaves them with a cliffhanger and musharingdum... (blah blah) they have to be reminded "whack for me" (order me a drink) which means knock on the bar to catch the Innkeepers attention. When the whiskey is poured from the jar they get the next installment of the story. That's the tradition where all the different versions originate from.