Well, I'm finally getting around to making the DIY CO2 system for my 30g. So far, I've got my two liter bottle(s). Caps drilled. So, all I need is my check valves and a 16oz bottle for the gas separator. I'm using airline tubing, I've heard that you should get co2 tubing, but also heard airline tubing works just fine. The tube has an air-tight seal right now, but I plan on putting silicone around it. And probably getting some bulkheads if I can ever find them around here. Shipping is what stops me from buying off line, its always more than the little miscellaneous item you need. Anyways, I'll go take some pictures of what I have so far.