I did this a while back but just had the notion to post it here.  Its my knock box solution to limited counter space.  I was using a home made box that I made from a wooden recipe box.   I just added a piece of wooden dowel across the middle of it.  It was fine for a couple of years but one day I had a brainstorm and went with it.  My Gaggia/Rocky setup is on the counter above my spring-hinged door that I use to access the trash barrel.  So I cut a length of dowel and fastened it across the expanse of the trash compartment, just inside and below the access door.  Now I just push the door open and knock the puck directly into the trash.