The human excrement component of household waste to the septic system is not problematic at all
It's the other stuff:
The grey goop from the "in-sink-erator" type of waste disposal
The alkaline-and-fat-heavy waste from the dishwasher
The vast volumes of "grey" water from washing machines & showers that dilute the poos-and-water mix in the septic system
The household cleaners, bleaches, shampoos, oven-cleaner residues - all that stuff
I have worked on drainage systems for over four decades and watched them develop in complexity as residential sections have become smaller and the burden of water and aggressive chemicals become larger
It doesn't have to be that way: Once the inspector has gone there's nothing to stop you bypassing the system for the "water" from showers, dishwashers, washing machines - just attach it to a hose and let it water the grass somewhere . . .
I have lived on rural small-holdings all my life and can tell you, hand on heart, that if all you put into your septic tank is shit, water, urine & toilet paper (and don't use chemicals to "clean" the toilet bowl, or run the water from the small wash-hand-basin into the toilet line to the septic tank) then you can have a simple, single-chamber, old-fashioned septic tank AND it won't need to be cleaned out for 20 or 30 years
I have seen the insides of dozens of them where old houses had toilets only into the septic tank and "grey water" through a fat-trap and sediment-trap system and then out to soakage. The "solids" in the septic tank build from the bottom up, the "floaters" sit on the top and are very soon full of worms. It can take 30 years for the solids to work upwards and the floaters to work downwards until there's only about 100mm of vertical space in between them - and the tank STILL works fine
What comes out into the soakage is a nutrient-rich liquid that is very low in volume as it's basically only a dozen or so toilet-flushes per day - maybe 100 litres? All you need if a few metres of soakage & some flax bushes for transpiration
Shit isn't a problem
Chemicals that kill the bacteria in your tank are a problem
(That, and Council's insistence that everything must pass through the "septic tank" system including shower & laundry water you could probably drink if you were stupid enough to)
In my own, un-permitted property I have what is effectively a hole-in-the-ground downstream of each of the two toilets. The soil is very free-draining and the water from a flush drains away in seconds. All that's left is shit and paper and worms. Each hole is the size of a Mini. I guess it might take 100 years to fill either of them up? The grey water just goes to keep some grass green
Excuse the rant