Big Freaking Water Rocket Launcher

I want to turn a 15 litre water cooler bottle (the non-deposit kind made of of heavy pop bottle plastic) into a big freaking water rocket.

This design is untested, use at your own risk. I for one don't plan on being anywhere near the launcher when I put pressure in.

Just uploading it for comments/ideas.

TODO:
-Release mechanism (in progress). The base design has spots for o-rings, and could operate by just letting it go whenever the pressure is stronger than the friction. I would l