We are the web's only supplier of The Kegging Part. This little gizmo turns keg coupler threading into a ball-lock post. It's not the only solution to this problem; just the best solution. Check it out:

Sure, it works, but you have no check valve. To disconnect your tubing you have to depressurize everything.

Perfect! Now you have a check valve in the form of a ball-lock post. It's rather silly looking and there are an awful lot of connections. I call connections "Places where leaks can develop".
If you want a real solution, it's The Kegging Part!
Nice. Simple. Easy to use.
As you can see, The Kegging Part also works with some soda siphons. It turns out that the threading is the same. Why keep wasting those 8gm CO2 cartridges when you can just use your CO2 tank? A 5 lb tank should be charge the siphon over 250 times! Save money! No waste to dispose of!