Is it okay for the septic system? This is a great question. Here is the answer. As long as the salt water purifier does it’s nightly purge somewhere else. Make sure it is not plumbed to discharge into the septic tank. Here’s the reason. Salt water changes the specific gravity in the septic tank. In short, the sludge that used to sink to the bottom, now can’t sink. It’s held in suspended animation where it will go out to the drainfield. And it will plug it. It has plugged pumps and pipes.
A tall tell sign that your tank maybe the purge is that everything in the tank looks blacker than normal. It will be obvious to me. I have seen this many time, and it can be corrected by pumping the tank and redirecting the nightly backflush of the purifier.