I read you post about the septic backing up. I would be willing to bet it is two things.

1) someone remomved the baffles in the tank (they prevent floating material from entering the drain field).

2) removed baffles lead to clogged drain field.

the only solution is to have the tank pumped and have the guy go into the septic tank and check out the distribution pipes, bet they’re clogged.

If the baffles were take off the only solution I know of is to have a new septic tank put it… unless you can find someone who knows how to jury rig a new baffle system. Typically they’re part of the concrete tank. Why people smash the baffles off is beyond me… you really got to be a knot head to do that.

If that is the problem you could go after the previous owner legally – putting in a new tank will cost a small fortune.