I happen to have finally received for Christmas a copy of Gabrielle Lanier
and Bernard Herman's new book (1997) on _Everyday Architecture of the
Mid-Atlantic, Looking at Buildings and Landscapes_ and in it they briefly
mention privies and barrels (pages 57-58)

summary:
Privies were commonly built in urban and village settings in the colonial
period but were rare in the rural areas.  (I guess Mother Nature was a
favorite even back then.)  They mention that barrels were used and many
were found in archaeological excavations in Philadelphia, Baltimore and
Wilmington.

"Barrel privies were inexpensively constructed, easily maintained, and
frequently abandoned when the occupants of the property changed.  Most
barrel privies excavated in Wilmington, for example, were simple hand-dug
pits; some were fitted with removable bottoms that probably facilitated
cleaning.  The barrels were closely packed on the outside with dense grey
clay to prevent contaminants from leaching into the surrounding soil and
entering the groundwater."

They also note (page 58) that wells could be easily constructed and lined
with barrels.

Here's a link to a summary of one of the DelDOT reports from which the
above data was derived:
http://www.deldot.net/static/archaeology/archives/D039.htm

        Dan W.