Another suggestion made to me by the "honey dipper" was to have a separate tank for your water softener backflush water. He suggests that there is a higher concentration of salts in the waste and this can lead to earlier septic tank failures. The salts can be highly corrosive which can lead to the concrete failing and the wire mesh and rebar to corrode.
What he suggested was to get a large platic tank, dig a pit, line the pit with stone, drill some holes on the sides of the tank (not specific on placement), and backfill with more stone around the tank. This way the backflush water will be held, the heaver salts and particulate would settle to the bottom, and the cleaner water would drain into the stone. When the 'honey dipper" comes back to pumb out the septic system, they also pump out the backflush tank and remove all of the deposits. Sounds good in theory, but I haven't heard of anyone doing this.
Terry