Although the lightbulb is overused, I believe when used in this instance it is far enough removed from the traditional sense that it doesn't seem generic. The lightbulb is the shape of the top of the tank, in case it wasn't obvious. The basic concept for the logo was to combine think (or thought) with tank. The lightbulb was the only universally recognizable symbol I could muster up for thought.
I know the typography needs work, but this is what I settled on temporarily.
As seen on: Visual Thinktank
Status: Client work
Commenting: Actively seeking critiques