Good thing, salt water and the cement box used for septic don't mix.We are on septic/leaching field, and my husband is not a fan of dumping salt water down the drain, as it could affect the balance of bacteria to break down our waste - I know there are varying opinions on this so take it for what it is. That being said, I'm not sure I'm going to be able to haul my salt water out to the curb to dump in the sewer for much longer. So a new house for me would be on public sewer/septic, and not a private leaching field.
Currently in my area, they are separating water softener systems and the septic because it caused a lot of problems with septic tanks. And as you know that is all salt.
On my auto water change system I drain it outside into one of the downspouts that goes underground and away from the house.