Bah! So it was all a joke! Well... let me get some input on this deco chamber in as well!
As far as strength goes... you could wrap the septic tank in duct tape several times. Just pick up a case of it at Costco, and whammo... instant structural strength improvement! Maybe you could also truss the tank up with some butcher's twine too...
I'm thinking that you might be able to line the Yak's pen with some of those little foot powered air pumps. When he walks around in it... he'll be helping pressurize the chamber! That should take care of the air compressor problem...
Heck, while you're at the tire store picking up the valves, maybe they have a couple air compressors lying around that you could pick up cheap! Just add in a couple pints of oil (synthetic is a marketing scam anyway), and you should be all set!
And just to make sure that everything is hunky dory inside the chamber... remember to add the canary cage.
-B.