What is known as an outside pool refers to gamblers playing against each other rather than against the house.
For instance, Old Liu bets on "sandwiched," while the show-off bets on "not sandwiched." The win or loss stays strictly between the two of them, involving neither the house nor anyone else. However, this style of play does not feature pillar hits—only sandwiched and not sandwiched—and the odds are fully negotiable. The official payout is double, but in a private game, you can set the odds to whatever you like, depending on mutual agreement.
"Brother, care to play a round in the outside pool?"
Chapter 463