To tank in poker means to take a long time to make a decision. A poker player will go into the tank when they face a big bet and they aren’t sure how to proceed.
You’ll often hear this expression used by poker commentators. For example, they could say something like – Phil Ivey has been in the tank for almost five minutes now after his opponent moved all-in on the flush-completing river.
Tanking is fine when you have a really difficult decision and want to think about the hand. However, excessive tanking, which some players are prone to, is often frowned upon, as it slows the game down. If players tank too often, you can even call a clock on them and force them to make the decision faster.
Not every decision requires several minutes, and players who constantly take too long to act can make the experience worse for everybody else at the table. On top of that, some players tank when slow rolling, which is something you should avoid at all costs.