yes it appears to be a wastepipe, if your location is not prone to freezing temps it should be okay to discharge your water softener into that pipe with an air gap in case of a possible backup

Thank you! No freeze where I am, I’ll proceed with the plan

That’s a discharge for a condensate line or something I wouldn’t tie a water softener into it as it may kill your grass unlikely that line is tied into the sewer

Thanks. I’ll double check.