250 gallon tank is pretty small.

"If it won't rot then it shouldn't go in the pot"

A septic tank works by microbial action. The bacteria in the tank break down organic matter and their waste, suspended in an aqueous solution, is drained out in a leech field.

Microbial action takes time, and the amount of time they have is based on water usage.

You don't want to kill the bacteria, they are critical to the tanks function. So don't dump an entire gallon of bleach down the drain. A little bit is fine (normal use) because it gets really diluted. You don't need to add bacteria pods or anything like that, just go take a fat shit.

Any dirt, most oils (unless soaped up first) plastics, will stay in the tank until they are pumped out. Too much of this will clog your drain field and you will have to dig it up.

Good pumping rule of thumb, One person = pump tank every 10 years for a 500 gallon system. So for you, every 5 years. For every additional person, divide.