Markit wroteI often read of people pumping out their septic tank and wonder why? (I know, get a life, right?)
My septic tank(s) are about 3 meters long and about a meter wide with 2 or 3 steps in them and the last step is open to the earth. Concept is that the waste is progressively rendered biologically neutral and then on the last step allowed to soak into the earth.
The problem is that not everything breaks down in the first chamber. It will eventually fill up with solids and need to be emptied (approximately once every 5 years, but it depends).
I think you can get almost complete breakdown if you constantly aerate the sewage water in the first chamber but having an air pump running 24/7 is more costly and complicated than just getting a truck to pump out the waste once every 5 years.
Markit wrote . . . can't even get at it if I wanted to as no access cover.
This drove me nuts when they were building our septic tank. Typical Indonesian short-sightedness. I had to become an expert in septic tanks within 24 hours so as not to get stuck with a basic design that would be a huge job to dig up and repair. It's not even that hard to add an access hatch.