Marco Lips offered up this Teaser, but didn't supply an answer. (Darn you, Marco!)

Mike Gempp posited that it was one of the big pipes connecting Teal Pool with the Saw Mill Creek Mud Flats/Tidal Impoundment, and we agree.

That said, the other answer — "probably the bottom of his coffee cup" did not sound that far-fetched.  Thanks to all who particpated, including Marco.