So according to this article the term came from swimming/diving. A swimming pool was called a tank, so going into a tank is taking a dive. No idea how reliable Slate is though
http://www.slate.com/articles/news_and_politics/explainer/2008/10/explainer_goes_in_the_tank.html
Swimming pools used to be called "tanks". So when people said the player "went into the tank", it was essentially the same as "taking a dive."
Since then, anytime you "tank" something, you're failing at something intentionally or spectacularly.