I've had some bad expierences with terra cotta pipes running into pit also but learned to get over it. Some of the best pits I've dug have had these things and usually they go quite deep.
Lets try that again. I too have had some bad luck with terra cotta pipes running into pits but have gotton over that one. We dig everything if it's on an old enough property and some of my best pits have had theses things.
Lou, We don't dig round brickliners in Baltimore with a terracotta pipe draining into them. Experience has shown that these pits are later generally post 1880s and tend to be quite deep the shallowest ones are usually about 18' and I have dug a few that pushed 30' Even digging behind early houses the oldest any of these have ever gotten was 1880s and many never got any older then about 1900. And honestly local bottles of that age do not interest me very much. It looks like a trend starting in the 1880s was to replace a small woodlined or barrel lined pit with a deep septic well behind many houses. Sadly they tended to build the newer deep brickliner through the original woodlined pit destroying it. If anyone ever wants to dig some of these deep brickliners there are plenty of them around town to dig. Maybe when I'm old and grey and there are no pontiled pits left I might get around to them...
Cast iron pipes are a different story they tend not to have much effect on the pit and usually flush out to the city sewer system.
I have dug around 2000 privies in Baltimore and have found some construction trends that have been quite accurate relating to depth and age of the pit. Also have found several city regulations on privy depth that confirmed some of the trends I saw while digging.
Round brickliners in Philadelphia with a terracotta pipe running into them are still worth digging as they usually do get old.