From the ArcaMax Publishing, Jokes Newsletter:
http://www.arcamax.com/news/jokes/s-367496-276486
A drunken man staggers in to a Catholic church and sits down in a
confession box and says nothing. The bewildered priest coughs to
attract his attention, but still the man says nothing.
The priest then knocks on the wall three times in a final attempt to
get the man to speak.
Finally, the drunk replies, "No use knocking, there's no paper in this
one either."