Seepage pit Q (insert poop joke here)

If you know where the tank is you should be able to find all the corners of it by probing with a rod(I used a piece of rebar vice grips and hammer as my clay soil was like concrete this summer)
The outlet "should be" in the center of the narrow side(usually4x8' tank)
The probe depth of the tank and any slope in the ground towards the cesspool should tell you if the concrete is an additional seepage field - if that makes any sense?

 

I gotcha, here's some highly professional sketches of my chit-uation The mystery structure is a good 30 degree angle to the tank. I know the tank is square to house as the lid was. And yes, we have 2 swingsets.... don't ask; at least they were free and I just had to disassemble, haul and re-assemble.

 

Any pictures of the concrete pieces?

 

It's possible they added leaching chambers or galleys to the pit.
The leaching field is dictated by number of bedrooms in the house. You figure in MA even back in 85 they had code requirements.

 

I'll post some when I'm brave enough to face the elements.... which means probably next week

 

This is the most likely scenario if my archaeology proves it is a true structure.

 

if it's small could be a D box or distribution box to lines. depending on topography my guys would put bends in to keep it deep enough and pitch. Easier than hauling in more soil...

 

Any chance you have a floor drain in the garage? I don't know if they were against code by 1985.
The other possibility if it's not part of septic could be a diffuser for basement sump pump. I remember my grandfather backfilling our septic tank when I was kid(probably around 1985) after sewer was installed. That house was built in the late 60's and had a drain tile system for the sump pump discharge. I had to disconnect the pump outflow and run it to the street during a turdfloater tropical storm remnant ~96. Lost my battle with the rain running 2 pumps and bucket brigade for several hours, hydraulic cement started popping out of the rebar/form knockoffs

 

Might be a case of the septic tank was ok but the drain field collapsed so they took and dug a new drain field and hooked into pre existing part of drain feild or into septic tank and left old one for a keepsake instead of ripping up more yard and additional expense. This was done at a house I rented. Not sure if it was the right way but that's how they did it.

 

No garage here unfortunately and no sump pump. I was in my good clothes so I haven't dug any further but the rain washed the concrete to give you a better view of one of the sides. That long piece I haven't found the bottom of.

 

Sure looks homemade cinder blocks poured together
If its that far open and doesn't smell like doo-doo it's probably not septic related.

What about gutters? any downspouts run to drain pipes?

 

Yes, all downspouts run underground to many different areas. This guy was nuts for that, as I learn of new outlets yearly. Could be a dry well for rain water? There are a a mess of drains under the deck that look to be disconnected over the years. You could be on the right track.

 

being a homemade tank that's probably what it is.
Could be all/some of the downspout drains blocked up over time and instead of paying for a hydro-jet they just abandoned them.

I'm surprised you don't have a sump pump figured for sure with a basement(looked like a bulkhead door in house picture)

 

Yes, no sump the house is dry except for March of 2010 when we had the "100 year flood."

 

Judging from the pictures you have posted I would say that you have indeed found Hoffa.

 

You need to call Heraldo. He'd find out whats in there...

 

I would guess that it would be a pit for downspouts also.

 

I reburied Jimmy for another 30 years