Join Date: Jan 2008
Either is fine.
The CO2 leak-proof tubing is fine, but is expensive.
PVC tubing (the clear kind that is normally used for air pumps) is cheap, but becomes brittle with time.
Silicone tubing is a little more expensive, but remains more flexible with time. It is slightly more permeable to CO2 than PVC tubing, but still negligible.
I use silicone tubing because I had it handy, and I like how it stays flexible.