I basically want to make a rocket, which one should i make?

Okay, so here's the basic plan, tell me what you think.

http://i36.photobucket.com/albums/e42/alexalex132/cannon.jpg

The first one has the reducers in the pneumatic compression chamber leading down to a small ball valve. The second one is the same except there is a large ball valve then the ...

Yeah, can anyone point me in the right direction for a design? should i use pvc pipe? or some type of tank like they used in the video?

I will make sure the joints will be cemented. But I want to have a nozzle at the end so it sprays the water out creating a lot of thrust in the other direction.

I have a bit of experience with making basic pneumatic spud cannons and I have a question. I need to make a pneumatic "launcher" like this one: http://video.google.com/googleplayer.swf?docId=6157101787435882287&hl=en

I made a simple version (potato cannon with an end cap with a hole at the end ...