Here we have to dig a test hole and unless water drains in a set amount of time, a septic tank is not allowed. We are on clay, so all new systems that go in are aerobic (Klargester), as they do not make the timescales. The Klargester we had at previous house needed an annual service and 6 monthly emptying of solids from solid tank. It did discharge clean water to the ditch though.
At current house we have three tanks in series that then drain via weeper drains under the field, two take solids, the third tends to catch any water that flows back in from the weeper drains.
We have only emptied tanks once when moved in - so 9 years ago. Since then it just seems to disolve itself and breakdown. We would not now be allowed this system on a new build.
My personal thinking is the best system would be a combination of the two - septic tanks to catch and disolve the solids (to eliminate 6 monthly empty) feeding an aerobic (Klargester) system to purify the water.
J