Richard Wollheim-
"An object may be characterized by the intentions, or lack thereof, of its creator, regardless of its apparent purpose. A cup, which ostensibly can be used as a container, may be considered art if intended solely as an ornament, while a painting may be deemed craft if mass-produced."
The tank isnt being "used" as anything. It is use-less, therefore it is art. If you put a stator as a weight on a pull string it then has a function. It would look stupid. Would be a conversation starter though...but not like a gas tank on your piano!! (wifey HATES it there)