Working well and fed right, I have gone 10 years with no issue, on several houses.
You absolutely should NOT feed them fat, grease, meat scraps, anything that doesn't come out of YOU. A disposal into a Septic System is begging for trouble.
Printed tissue is also a DO NOT, the ink doesn't break down supposedly.
If you haven't fed them Rid-X or similar from the start...DON't. This from a Minn. Septic guy, he says it aerates the tank and pushes solids out.
I never have used it. That which comes out of you is sufficient..........
I have only lived south of Atlanta, your results may vary.