Back many years ago in Virginia, I took my date to dig with me in a
privy that was washing out of a roadside embankment. It turned out to
be a revolutionary-era tavern privy, loaded with busted dishes. As we
ended our romantic ramble through Virginia history, we noticed a
nearby highway historical marker titled: "Cornwallis' Movements."
One presumes the reference was to Lord Cornwallis' military
activities, and not to the subject of our day's frolicking.

There should be a big difference between city and rural privy vaults.
City privy vaults were typically cleaned out periodically, so that
they will mainly reflect their last period of use, or the
installation of plumbing.  Country privies, by contrast, could be
moved if the vaults became useless. This means that you should find
sealed and stratified contexts in country privies.  Curiously,
however, we seldom see more than one or two privy pits on farm sites
around here.  Is this because country privies were less well lined
and therefore able to leach?