Poly Tubing Leaks - what is the secret?

There should be a small piece of tubing ( insert) that fits inside the poly. if it's a standard type compression fitting. The tube keeps it from distorting.

What is the secret to making good connections? There is no separate ferrule - it seems to be part of the threaded connector. There are no inserts that go in the tubing ends to stiffen the tubing at the joint. I know not to over-tighten the connectors, and I try various levels of tightening, to no avail. I don't think it matters how far the tubing sticks out of the connector before the connection is made, does it? Is there some other variable I need to alter? Why do these connections seem so darn touchy? Even the RO filter change instructions say to keep going back to check for leaks, like they think the odds of failure are high.

Thanks, Teffy

Get the proper fittings. There should be an insert. You may also want to consider using copper tubing and the proper fittings for that. Less chance of a problem long term.