I don't know about the guys that dig them but the some of the ones I find underwater are certainly usable. I have some fullt intact ones that I used a long stiff wire to clean out the clogged stem with. They are near perfect.
The ones I have found in civil war camps are usually pretty close to original condition.
Sometimes the kaolin or unglazed clay ones erode a bit but the glazed clay ones are typically like new.
Thanks for the reply to the PM. Still curious about how long you've been in the Portland area--did you ever hear of "Der Outen Hausen" magazine or a similar name? Is there an active bottle collectors' club there now?