Ours backed up recently. The problem with ours was the leach field had failed. On top of that we found it to be an illegal leach field installed by the seller I bought from. It is only about
40 feet long and they plugged the end pipe with a cap....so basically it didnt have enough capacity to handle all of the effluent water coming out....eventually it backed into the house... for a few years it worked and actually leached out, but now it is junk.... I may be looking at a $25,000 bill for a new chlorination system or sand mound....New septic systems are getting harder to put in because of strict regulations and soil tests....it is all a bunch of "crap" if you ask me!
Few pointers:
1.) dont use a sink disposal
2.) try to run your showers and bathtubs, and washer to a separate "gray water" leach bed that doesnt go through the septic
3.) dont flush heavy paper towels or sanitary items
4.) get your tank pumped every year or so to prevent your leach bed getting backed up or clogged.
5.) always check your baffles for clogs before you assume the worst. could be a simple fix.
6.) make sure your lid is above ground with a good riser seal to prevent ground water from entering.
Hope you have better luck than we did.