The Scoop on Poop: There are septic tanks and septic fields:
Septic Tank.....as they are called where we used to live. In Northern Manitoba at the shore of a huge lake. These are tanks with no outlet. Like an underground submarine with a lid on the surface you can unscrew to see how full it is. They get filled up and have to be pumped out (every 3-4 weeks, but varies greatly with number in household running water). All water goes in there. So for about $50 a crack the truck comes and sucks it all out and dumps it in a designated "pond" away from the lake, which is apparently treated with chemicals.
Septic Field.......Where we live now (right on the Atlantic). But also common inland, but NOT near any lakes. These I BELIEVE are also tanks, but they don't get pumped out. Well, they can be, but as posted, some may last decades before needing any attention. Liquids do ooze out from the tank (all underground, of course). Solids do accumulate, but you can use treatment (powder of sorts) that you flush down the toilet weekly/monthly, depending on household numbers. We are away a lot of the winter and I am 2 months each summer, so we may never have to get it "pumped out". We have a well as well, so the only cost really is the electricity to run the well pump.