[MrBasse]

I can't say for sure about other brands, don't know why they would be any different, but with the Parker fittings it was reccomended while I worked there to insert the tubing fully and then pull the tubing with some force to seat the barbs in the collet. The way the push to connects works is by making use of the pressure in the line to clamp tighter and tighter holding the tube against an o-ring. You should be able to run these fittings almos to the burst rating before the tubing will let go.

Do as others have suggested, cut your tubing straight and insert it as far as you can. ThEn pull on he tubing gEntly to seat the barbs into the tubing. You really shouldn't push in and repeat over and over again as the barbs will damage the tubing slightly, weakening their overall grip. One solid push and then a gentle pull on the tubing should suffice.