In Philadelphia there are 18th-C privy deposits consisting of many hundreds
(sometimes thousands) of ceramic and glass objects that appear to have been
deliberately placed to create "percolation" fills, apparently as part of the
process by which privy vaults were brought into compliance with city regulations
from the 1760s limiting the depth of such facilities.  
 
These deposits become less common in the 19th-C, except in cases where a
"double-shaft" arrangement was constructed - the diameter of the shaft being
stepped-down with a "percolation" fill placed at the intersection, supported on
planks over the lower, smaller diameter  portion of the feature.  One expects
that this arrangement allowed odiferous liquids to settle and be less noticeable
to the users.
 
Also, Dena Doroszenko and Richard Gerrard presented a paper at the 1991 CNEHA
conference at Newark, Delaware, entitled "Privies and Mass Disposal Practices:
An Example From Perth, Ontario" which offered the possibility that mass
disposals could have resulted from housecleaning events associated with serious
illness or death in the household.  An imperfect understanding of disease
vectors could have produced such practices.   I am reminded of the story of the
_Velveteen Rabbit_ in which all the toys and linens were burned after the
child's illness. 
 
Regards,
John
 
 
John P. McCarthy, RPA
Sr. Project Manager - Cultural Resources
Greenhorne & O'Mara, Inc.
9001 Edmonston Road
Greenbelt, MD  20770
301-220-1876 voc
301-220-2595 fax