It sounds as if you have two septic tanks that drain into a Leachfield or drainfield.
Not sure if this answers your question.
I have a cottage in Northern Michigan built circa 1945. When we had to move the cottage back from the bluff it was placed directly over the septic system.
When we had it pumped the guy said they were "Schimpke tanks". I'm not sure of the spelling. They are two round, concrete tanks about four feet across and four to five feet deep, connected by about a 4" opening at the top. The second tank had become so full of fine roots he wouldn't try pumping it as he was afraid it would clog his unit. The small opening between the two tanks had become plugged, hence the need for pumping I guess.As I recall the second tank had a similar 4" opening toward the top that headed out to the drainfield. Haven't had any trouble since but we are VERY careful about overusing the system. We had one toilet and two sinks emptying into it and that's it. We don't flush on every use and we have our shower drain into a hand dug rock pit in the sand.
Has anyone ever heard of this type of system?
There is a type of septic tank, called the Imhoff tank, and sometimes called the Emscher tank.
The Imhoff tank is designed to separate the sludge from the flowing sewage.
the imhoff tank was used in I believe in more commercial settings, I don't really think it was a system use in a home setting.
I worked and operated a wast treatment plant in the mid 1970 at waht was one time a Air Force Station,
In that the main clairifer was a Imhoff tank, and like in the link above the picture there is a open bottom V shaped channel that the effluent ran through separating the solids out of the effluent the bottom of the tank was cone shaped with a pipe connected to drain off the sludged that accumulated to drying beds that were over a sand bed that then contained a drainage field that lead back to the lower settleing tank system,
The Imhoff tank used antiaerobic principles to break down the solids,
Then in that system there was dousing tank (automatic syphon) Kinda like a toilet flush, and then it ran the sprinkler system in the trickle filter,
A tank filled with rocks and a sprinkler to distribute the effluent evenly over the surface, this was a simple aerobic treatment system, as the rocks (about 2 to 3") in size would grow a slime on them and the effluent was sprinkled over it to be worked on aerobic bacterias, there was an air tunnel under the tank to feed it oxygen,
then in to final settling tank with return pumps to take any thing that was settled out back to the top of the system to be ran through again, and finally a chlorine treatment and holding tank, before being discharged.