Hmmmm.....I (thankfully) have never had concern of a blockage,but I would think that "nothing" would come out at all
Hopefully someone with more experience in that area will chime in and give you some answers.
The only other thing I can think of that would be causing the diarrhea would be the kind of treats he's getting? Or maybe he's getting into something (like the garbage) that you are not aware of?
Canidae is a great food and a lot of dogs do very well on it, but my last girl had very soft stools when we were feeding her Canidae ALS. We switched to Innova and the problem was solved. She also did well on California Natural (both the chicken and lamb formulas).