I have only been kegging for 6 months. For simplicity, I use the same tubing for both CO2 and beer. From Amazon: ATP Vinyl-Flex PVC Food Grade Plastic Tubing, Clear, 3/16" ID x 5/16" OD, 100 feet Length . It is food grade and good up to 55psi. It is clear, so I can see if beer is backing up...