lookindown,
I think, back in the 60's, that was a common practice all over the country. (60's and earlier). The old farm where I grew up, which had a few extra outbuildings (homes for the hired help), all had those tanks sunk into the ground. Then, when they went with septic tanks, they were considerably smaller than the ones we build now - with no drain fields - and then they started the "split" septic tank (with a side for solids and a smaller side for the overflow liquids) - and still no drain fields - and then the type they use now - larger, with drain fields.
However, Pa went a step further and started the sand mound system - they cost 20,000 dollars and more to put in, and only work for 4-5 years. While Pa doesn't have javelina, etc., it does have other animals that like that sort of thing, so, with the new sand mounds failing without anyone even knowing for the first year or so, the animals that like that sort of thing, start coming around much more.
I have to laugh about Haitians pooping in the street. Even now - as we speak, there are thousands of streams that have septic from towns running right into them, without too much benefit of filtration.
And, our farmers, for years, spread manure on their fields, and our US powers that be thought they had a better way - it goes into a huge (and of course, expensive) tank, with a system like a large sewage treatment plant, until it has no solids left, and then is "sprayed" onto fields. It's horrendous.
Plus, even though you have to have an approved septic system - does anyone know what happens to the stuff that septic tank cleaner guys suck out of your tank? Surprise - it gets stored for awhile, and then is sprayed onto fields. Legally - so, anything that eats grass, whether it is straight grass, or eating animals that feed on animals that eat grass - are exposed to human fecal pathogens.
Beth