I modeled this tank for one of my classmates who decided to build a Bubble-Bot. I designed it such that to minimize the volume of material used but also to use as little solution for balloons as possible.

The shape of the tank was created in order to produce as many balloons as possible and much fun with a small amount of solution for balloons.
As every time I published a STL version of the project, which you can print immediately, and also a SketchUp file for those of you who want to customize my project to suit your needs .