I've used push fit connectors from the
Festo range in my system, bought locally and rated at 10 bar air. As said the tube needs to be stiffer nylon type which gets very non compliant as the tube size gets bigger. The two items in my system, (HDD waterblock & PSU waterblock), share the same loop and don't require high flow rates. The tube is 6mm OD about 4.5mm ID is fairly compliant, easy to route and work just fine.
