I've been trying to use an Ander Lign compression fitting to connect a 3/8" OD plastic tube to an Ander Lign tee. I tighten the nut very tight, but the tube can still be pulled out of the fitting fairly easily. I've followed the installation instructions exactly. What I've noticed is that the brass insert (which came in the package with the fitting) is only about 0.17" OD while the plastic tube is 0.25" ID. Any comparable experiences out there? Is the solution just to use the next size larger OD insert so that the ferrule has something to squeeze against?