Zezmo, I was concerned with the same before trying it, fwiw. As long as the canisters are producing gas theres no issue, but there will be some flow into the mix until the airline fills with gas. Check valves or a separator bottle is plenty of saftey, but not necessary assuming your mix bottles have space for a little water. I use a small on/off valve to close the line for mix changes, let the gas build up a little, then open the line. Works great.