The septic system may be like grandma's. A tank in the ground to "settle" the stuff, with a cistern pump out under the elm trees. When you pumped the tank out to make room for more drain water, the chickens came runnin' to clean up the lumps. By the time they got done, there was nothing but chicken sh*t under the elms, but that was already all over the place so that was "normal sanitary" without separate treatment.
Life on the farm was really healthy 'way back when ***
Actually, granny's system wasn't all that crude. The settling tank provided time for the "sewer biota" to digest anything dangerous, and pumping the "processed water" out on top of the ground was very little different in actuality than seeping it out a little at a time in a "more modern" septic field with fancy porous pipe and all that stuff.
The only thing changed with a "more modern" system is that you didn't have to have someone work the pump handle the 436 strokes (I counted it several times) it took to spread it out once a week or so.