While the privy thread may be winding down, any thoughts on the below
will be appreciated.
 
I recently exposed (but was unable to excavate) a brick privy vault
near St. Joseph, Missouri.  Only the top remaining 6 runs of
brickwork were mortared and the remaining bricks were merely
stacked atop each other.  What seemed to be to be an excessively wide
builders trench (about 70 cm) was also present.  Soils below the mortared
courses were thick nasty clays.  Any possibility that the trench and not
sealing the lower bricks was intended to help the vault perk?  Sadly,
I don't know if any water-proofing is present on the interior
surfaces.  Obviously, the mortar was not required as the vault was in
great shape despite dating to near the turn of the century.
 
Thank you,
 
James Harcourt
"Agency" Archaeologist