Well thanks for all of your quick responces. Most of it seemed positive which is always nice, here are my answers to some of you questions and comments.
1. Rubber membranes and cut out milk jugs seem like they would require far too much power to burst. Im not looking to kill bulls at 2000 yards. However badger's advice of using heavy duty trash bags seems possible. I plan to just have fun with trial and error for a little while until I find something perfect.
2. Last man alive, not too sure what you were talking about with your video plan. Dunno what a Nerf milsim movie is, if you want to try to explain it to me that would be fine.
From all of your posts I got the idea that you all wanted to have a better idea of what the gun might look like in the end. So I decided to put a little more meat on its bones (make the tank and put it on the valve) to give you a better idea of what im shooting at.
Here she is!

Next to a titan rocket for size comparison:

It clearly still has some work do be done, I need shrader valves for both the tank and the tiny burst chamber. Also it needs a barrel. None the less this project is well on its way.
Questions, comments?
-sponge
When in doubt, make a huge nerf cannon of death.