Most municipal water districts run wastewater and stormwater. Stormwater in towns with rivers run that back to the river (almost always), while kitchen sink water is sent to the wastewater treatment plant.
I have an auto water change system and it dumps into the kitchen sink drain. I do have a check valve just before it dumps into the drain just in case. I have been doing this over 6 years without an issue. Since the kitchen sink is the most often used the water dose not stay in the drain very long. The drain pipes are also PVC so I doubt the salt will cause an issue.If you do this manually just run the faucet after you dump it down the drain for a minute or two.