I have no objection to the contention that barrels were used for privy
liners, I think thats a reasonable conclusion.  However, I seem to remember
the original query suggested that the barrels in question measured 2-2.5
meters in diameter.  No too big  for a privy, but I think a more likely
interpretation would be a stave-built cistern.
 
At the Trombley House site in Bay City, Michigan, two such features were
excavated.  Vertical wood slat sides, wood plank bottom and iron hoops around
the exterior.  I don't remember the diameter but 2 m plus sounds about right.
 One was built off the corner of a ca. 1840 residence, and the other was
built adjacent to the rear dripline of a ca. 1880 addition to the same house.
 Each probably about 4-5 ft deep originally.  Both were ideally situated to
catch rainwater run-off from roof and were located in traditional cistern
locations.  Neither showed any evidence for privy use.
 
Reference: Excavations at the Trombley House (20BY70): A Settlement Period
House Site in Bay City, Michigan, edited by Earl J. Prahl.  The Michigan
Archaeologist, Vol 35 (1989).
 
By the way, my original flame about fear of units more than 1.2 m deep was to
be taken somewhat tongue-in-cheek and had more to do with the current state
of litigation than archaeological moxie.