Mysterious feature - old sewer?

Hope this isn't too OT but I thought someone here might have an idea for me. I'm currently renovating a 100+ year old brick building. Immediately behind the building, I'd noticed some subsidence in roughly an 'L' shape when I bought the property. Yesterday, I finally got around to taking a shovel to the loose the sinkhole that had been forming (over years) in the lower leg of the 'L'.
In the ground (subsurface) is a brick retaining wall along one side of the lower leg of the 'L' with two sewer pipes sticking through it. The pipes are about 12-16" below ground level and appear to have originally terminated there (inside the 'L'). We've dug five feet down and have yet to reach the bottom of the retaining wall.
My initial thought was that this was a sewage pit that emptied into one of the many caves or underground streams that exist in the area. This occurred to me as a bit fanciful and doesn't necessarily explain the 'L' shape. Someone else however, has suggested that it could have been an old backfilled septic tank. The latter idea seems a bit peculiar, though. A septic from the early 1890's, made of brick with no means by which to drain? City sewer has been available here since the dawn of time and the functioning sewage pipe for this building lives 6-8' below ground. To my knowledge, there wouldn't have been a method to empty a septic 'tank' in the 1890's so there would most certainly have been capacity issues if this were true. This is not to mention the stench it would have generated, esp. given it's proximity to the building.
Any other ideas? I checked an old map (1948) at City Hall and there's no record of another (above-ground) structure having ever been in this spot. The lower leg of the 'L' is about 6' long x 4' wide and the back of the 'L' is approx. 9' x 4'.
It's shape, size and the construction of the aforementioned wall effectively rule out any prospect of it being the remains of an outhouse.
I'm stumped and the backhoe doesn't get here until next weekend...
-BB
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Sounds like an old cistern.

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If you are sure they are sewer type piping, they could be lines to an old septic tank which would have been fairly large or a dry well that took storm drainage away from the building. Almost lost a backhoe when the heavy bridge planks covering an old abandoned septic for a school finally rotted enough to start to cave in. They had just tied the building to the sanitary sewer system and left the old tank in the ground.
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Have you tried contacting your local historical society? Could be they would have photos or other records of the property. Sounds like a mighty sturdy structure - old root cellar or "summer kitchen" with a cistern?
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In my house, built in the late 50's, the basement drains run into a pipe that exits into a dry well build with losely stacked bricks, with no mortar, in the front yard. The septic system is in the backyard and the rest of the house is connected to that.
So as someone else said, it could be an old, filled in, dry well.
dickm
wrote:

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