The Grauniad’s coverage of the fascinating World Chess Championship has frequently used the idiom in the tank to express that one of the players is behind and is taking up a lot of time thinking about their terrible disadvantage. I am totally unfamiliar with that usage—to me, in the tank means that the player (or team) in question is deliberately losing.
I think I have seen the verb tank used both for intentional and unintentional losing (although not in a close loss), but in the tank to me is always an allegation of corruption.
The OED has both, but the corruption-related one is a sports-specific term, and the non-deliberate phrase applies to more general failure, f’r’ex stocks, industries or personal lives. They don’t say so, but the usage is similar to in the toilet, and may be related. It’s possible that the version that is not an accusation slipped in to chess description because chess is different enough from other sports (if it indeed is a sport, which it probably isn’t, but the Grauniad coverage is under the sport heading) that it didn’t immediately strike the commentators as inappropriate.
How does it sound to y’all? Does it matter if the phrase is broken up—saying a player is in to the tank or deeply in the tank or something like that?