Another reference relating to nightsoil and privies:
 
Tarr, Joel A.
1975  From City to Farm: Urban Wastes and the American Farmer. Agricultural History 49(4):598-612.
 
The article concerns nightsoil collection from city contexts and use as manure on agricultural fields.  I recall that the earliest privy (post Civil War) in Kinkeadtown has evidence of being "dipped" at the very base of the shaft, but the practice was discontinued later in the privy's uselife, and later privies on the same lot were not cleaned out.
Nancy O'Malley
Department of Anthropology
211 Lafferty Hall
University of Kentucky
Lexington, Ky.  40506
606-257-8208