On Wednesday, October 29, 2014 4:42:24 PM UTC-4, Tekkie® wrote:
J Burns posted for all of us...

I think a good septic tank has two chambers. The holes in the partition
are at midlevel so neither the sediment nor the scum enters the second
chamber. The second chamber drains at midlevel, to avoid sediment and scum.

That minimizes solids in the drain field, and there's evidence that it
keeps waste in the tank long enough to kill pathogens. I'm waiting for
some town to make drain fields obsolete. Just use a perforated pipe to
distribute the purified waste water on the lawn. The town will become
famous for the absence of sewer bills, the green grass, and the sweet
smell of success!

No chambers, baffles at different levels for incoming and outgoing.

--
Tekkie

Around here I've seen them as J Burns described, two seperate halves,
built out of concrete blocks, no bottom. IDK exactly how the water
moves from one half to the other, but would suspect it may just be
that the cement blocks are not completely cemented together, continously,
etc. The heavier waste was in the first section, mostly liquid in
the second.