On Wed, 15 Aug 2018 15:35:34 +0100 (GMT+01:00), Jim K wrote:

It's a two-chamber (two-manhole) septic tank, with an outflow of
treated water (guess where it goes!)

"Treated" in what way?

Settle ment and anerobic digestion, like any other two chamber septic
tank. The out flow isn't particulary pleasant but it's not raw
sewage.

Going straight into the land drain? Yum!

Define "land drain". Is that: A system of buried perforated pipes
designed to remove water from the land. Or a system of buried
perforated pipes designed to distribute water into the land?

--
Cheers
Dave.