you can use wir line tubing however, that tubing is subjrect to erosion from the CO2. better to buy the silicone tubing made for CO2. they stock it at petsmart and it isn't much more than reg tubing.
I use this for water cooling in my computer only 7/16th ID . Look for (PVC tubing) -Masterkleer tubing.
I did not check the diameters of their tubing available....
Tygon is too expensive and pretty similar you can get it there as well but it is more expensive and more porous but a bit more flexable (good for tight bends inside a computer case) lol.
The CO2 tubing is black and supposed to be good stuff. He sells it for $.99/ft. I'm running pressurized on a 110g, so who knows if I am losing any through the tube or not?
Anyone know if polyethelyne tubing is ok? I had some extra from some other projects (tubbing from lowes), its vey rigid and heavy duty so I figured it would work. Not easy to work with though since its rigid. Cant remember off hand if its hdpe or ldpe.