What I know as a dry well is a large tank with holes in it. You run your sewer into it and it takes the place of a finger system. It works in sand probably not in less permeable soil. We had one when I was a kid. It was built of concrete blocks laid with a space instead of vertical mortar joints. It was circular and it could be either capped with a slab or brought in like an igloo.

I am not sure if they are ever used any more. It might not even be legal.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.