Ok.. here is how I personally built mine. Others probably have done things a bit different but mine works all the same. : )
Needed:
1) C02 Tank (mins is 20oz got from wal-mart)
2) Universal Fill Adapter ( http://www.sakworldpaintball.com/ unfilad.html )
3) Nipple Compression fittings (screws on fill adapter)
4) Industrial size aquarium tubing (any air/gas tubing would work - also if you have paintball shop they sell a "remote hose" which has build in fill adapter and tubing and a regulator but is more expensive than my total cost)
5) container for actual "chamber" (most people seem to use plastic 5-10 gallon buckets like from home depot and such but i used a water container that had perfect hole already - for picnis and such)
6) aquarium silicone (found at most pet shops)
Work..
connect fill adapter to tank, fittings to adapter, hose to fittings, hose to container silicone any "open" areas and thats basically it. It would be alot easier to buy that remote hose i mention but since I don't have a local paintball shop was easier and ALOT cheaper for me to order the adapter i needed. Hope this helps someone. reason I built this chamber is so I could pre-kill large prey in a more humane way than just wacking them on a hard surface or other various methods. this one seems much more humane and painless. thanks for looking