my last house there was 3 chambers with an airator in the middle chamber, not good for swimming in at all…
This is what I typically see in my area. A tank with a baffle on the inlet and outlet side.
old school there…
used to go to a hunt/fish camp that had a 55 gallon drum…one inlet pipe one outlet pipe…fancy stuff there…
Yep! They still find them here in N. GA. mountains for older residential homes. The super fancy ones have two 55 gallon drums… 
I remember back in the early 70s’ building a school in the boonies. my employer would give us a house trailer to put up the men for a year while building the school, so we’d have the excavater dig a big whole in the ground for the sewer and when we demobilized, just backfill and hide the sins. LOL
I don’t think we would get away with that today. 
the good old days…
this was in the pennsylvania hills buried beneath the moutain laurels…supprised those boys didn’t have a still up there…
Pretty sure it was there. You just didn’t see it. 
That is there style of my tank, minus the lid handles.
If your handles are rotted off, you can use a hammer drill with Taocon screws and fasten new handles on. I use the presidential election every four years to remind me to have the shit pumped out of the tank. 
We have what Marcel posted:
don’t swim in that one either Larry …