I am setting up a new tank and will be doing the same thing. I'm not sure I've seen the design you're talking about, but I've seen some ideas around on various sites. I have a 10 lb pressurized CO2 cylinder w/ MMM regulator, needle valve, check valve and bubble counter. I decided it might be fun to do a DIY reactor, so... I started looking around for something I could use. Then I found a cylindrical plastic bottle that currently has plant food (which I will find a new home for). The approximate dimensions are: 12"L x 3" Diameter. I will need to silicone seal the lid so no CO2 can escape, but I suppose the best way to do this would be to run a tube from the top of the bottle to the powerhead/tank. The other line should go into the side of the bottle, down below the bio-balls, of which will fill the bottle about 3/4 of the way. For tubing, use the CO2-proof stuff, or whatever they call it -- its cheap and if you have to buy tubing anyway, buy this stuff. I saw some on azgardens.com and I'm sure it can be found elsewhere. Sorry for the long post and for rambling -- this is more or less my thoughts outloud, but hopefully they will be helpful to others wanting to do the same type of thing. Cheers,
-Ryan