Susan,
        The barrel feature you describe may be a privy.  Although I have not
excavated such a feature, I have heard of old barrels being used to line
privies.  I believe this type of privy construction is discussed in an article
by Bruce Cale in the 1985 vol. of the Symposium of Ohio Valley Urban and
Historic Archaeology, called Pivy Constructionin Zanesville, Ohio.
 
  Hope this helps.
                  M. Jay Stottman
                  Kentucky Archaeological Survey