According to mike :
Im trying to figure out how septic systems work. I moved to PA recently and
everybody here has septics, including me. If anyone could help clear my
mind, that would be great.

I have a big tank for the liquids, and another smaller tank next to it for
the solids...and then like 30 feet away from those tanks is a big sand mound
with plastic vent thingees sticking out. I also have a septic pump.

#1, i dont understand how the tanks can distinguish between the solids and
the liquids. like how does it know which tank to go into?

As the sewage pipe leaves the house, it first goes to the solids tank, where
the heavy bits sink to the bottom, and the light bits float. There's a pipe
from the solids tank that has a baffle that "skims" the surface to keep the
light bits in the solids tank. Then, the liquid overflow from the solids
tank goes into the liquid tank, where the liquids are kept for a while. In
both tanks bacteria are busy trying to break the stuff down.

After going through both tanks and being acted upon by bacteria, the water
is routed through a series of perforated pipes in a sand bed ("leach field")
where it's distributed into the ground. By the time the water makes
it to the leach field it's pretty clean.

Most septic tanks, at least around here, are one big tank with a series
of baffles in the middle so the "upstream" half is the solids, and the
downstream half is the liquids.

Two tanks with solids separation are required to prevent solids from
going out into the leach field and plugging the perforations.

These systems are usually a simple gravity feed (meaning the sewage plumbing
in the house is higher than the tank, and the outflow of the tank is higher
than the bed).

In your case, obviously some or all of your drain plumbing in the house
is _below_ the tank, hence you need the septic pump.

Needing venting on the bed is a little unusual, so it might not be
exactly as described above. Might be something needed to ensure
that your septic pump doesn't overpressure the bed lines and pop
them apart.

Septic tanks need periodic cleanout if they're used more than
occasionally. Mostly to remove the solid buildup, and as such,
you can often skip cleanout of the liquid tank. If you know
when it was last cleaned out, remember to get it done again in 3
years later, and ask them to tell you whether it needs to be
done more or less often.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.