How do I tap a U-System keg?

[rth]

So, I have a U-system coupler, and a full keg of Guinness Stout (and a room full of thirsty coworkers). The keg coupler does not recess far enough into the keg socket in order for it to lock into the keg.

Yes, the coupler handle is in the "up" position, so the plunger in the coupler is retracted. But when I place the coupler into the keg socket, it doesn't seat far enough to allow for it to lock into the socket like it's supposed to. (I can see the angled grooves which would allow the coupler to "screw" into the keg socket. But the grooves on my coupler are a full 1/8" above the grooves in the keg.)

What's the trick to tapping a Guinness keg (U-system)?

Do I have to lean on the coupler somewhat in order to put enough pressure so as to get the coupler installed? If there's any residual pressure in the keg, it's going to spray all over the place while I'm trying to seat the coupler correctly.

In other words, I cannot get the keg coupler "deep enough" into the keg socket so it is able to lock into place, there by allowing me to drop the coupler handle and tap the keg.

Is there a secret to this?

Thanks for all the help.

--Bummed at the lack of Guinness here...