In The Barrel Definition

Origin of In The Barrel

• Attested 1950s.Presumably from a bawdy military joke, featuring a barrel with a glory hole , whose punchline is “It's your turn in the barrel."The joke has many variants and embellishments, but the kernel is: a new sailor is being given a tour of the boat, and is shown a barrel with a glory hole, which they are able to use any time, except Tuesdays. When he asks why not Tuesdays, he is told: “Because it's your turn in the barrel." Other hypotheses is that it is derived from like shooting fish in a barrel , or that it referred to a form of punishment in which the malefactor was confined within a barrel.

  From Wiktionary