Slow drains, a smell in the yard, or a pumping bill to check.
What a septic tank and drain field do, how often pumping is due, the warning signs of failure, and what pumping and replacement cost. Never open or enter a tank.

What septic pumping is, how often, what it costs, and the warning signs that mean repair.
Pumping price by tank size and region, extras (locating, digging, risers), and a fair quote.
What a new septic tank costs installed by material and size, and why the drain field is the big number.
The signs a system has failed, repair vs full replacement, and the fair price range.
What the drain field does, the signs it is failing (soggy ground, odor, slow drains), and what repair costs.
A labelled diagram: house drain, tank, baffles, outlet, drain field. Recognition so the reader can follow a pumper or inspector.
What a septic tank is and does, in plain words, and how to tell if your house has one.
What a riser is, why it lowers pumping bills, and the price. Never open or enter a tank: gases can kill.
What 'septic safe' means, what to avoid flushing, and the price difference.
Interval by household size and tank size, from EPA guidance; what happens when you wait too long.