The fittings are called "Push to Connect" and generally, in our industry at least, use 1/8 or 1/4" (OD) polyurethane, polyethylene or nylon tubing.
As was already mentioned, cut the tubing, CLEANLY and reconnect it. A good, straight, square cut is important. Don't use your wire cutters or dykes and please don't double the tube back on itself and use a pocket knife to try to slash through it. Use a sharp, straight edge blade. A new razor knife works well for this. If you deal with the tubing on a daily basis, they make specialized tubing cutters that work great.
Regarding the pressure, PTC connectors will take a lot of pressure before they blow apart. And they shouldn't "release enough". It either works and doesn't leak, or you have a bad piece of line or a bad fitting. I have seen haunt vendors use the wrong size line in a PTC fitting, rather often actually. IE, they had a bunch of 1/4" fittings, but got a great deal on 6mm line. 6mm does not fit SAE fittings well, at all. PTC fittings seal on the outside of the tubing so it is imperative that the correct tubing be used with the correct PTC fitting.
If it still leaks, check to make sure the PTC fitting is actually wrench tight in the valve / regulator / etc. We got a bunch of Dark Raven and Hazard Room stuff last year that almost nothing was tightened down. In fact, I plugged in the exterminator that we got from Hazard Room last year and one of the fittings promptly blew off of the valve. It wasn't even finger tight, let alone wrench tight. I haven't seen many PTC fittings that don't come with sealant already on them, but they are out there. Make sure the fitting has either pipe dope or (preferably) teflon tape on the threads.
The elevator motion simulators that I just finished building for my place utilizes a total of 210 PTC fittings. Not a single one of them leak.
Operations Manager & Technical Director