Right, so after fixing the issue with my Q/D - yup, managed to wash out an o-ring out of the top of the screw top of the Q/D and now have a new one - I reconnected the picnic tap perfectly fine this afternoon. Then, when trying again tonight it started leaking from the bottom of the Q/D.
So here are my complete kegging rookie questions. Could the following things have caused beer to foam out the bottom of the Q/D:
1: massively over-carbed beer, because it most certainly is now - oops!
2: overly tight screwed on top part of the Q/D - do I need to bac that screw off a bit?
3: or have I just buggered the seal on the post somehow?