[gloob]

Whatever number happens to mesh with the poster's predetermined position on the matter. If they think that HFT isn't "real work"[0], they'll set the level low. If they're a free-market fetishist, they'll say the tank is indefinitely large.

Metaphors are rarely a useful approach to understanding something.

[0] An amusing position for a programmer to take, considering we make completely intangible stuff while spending hours a day sitting on our asses, but one that a lot of people on this site seem to hold.