How can I get a printer to show in the Dock?

I have two printers, a Canon Pixma and an HP 3200 Laserjet. The Canon icon always shows in the Dock, and until recently, the HP did, too, but recently it's only been appearing when I select Print from the file menu and choose the HP.

It would be convenient to put it back in the Dock and have it stay there permanently. However, after looking in System Preferences and searching the Apple database, I didn't find anything that told me how. I've been using this printer (which has a Gutenberg driver, if that's relevant) with OS 10.6.8 for a couple of years and it's always been there. Anyone know of an Apple article that tells you how to restore a disappearing icon? Thanks!