I have a waterline from a whole house watersoftner dumping into a open ended 1 1/2" pvc septic line that connects to the main septic line coming from one side of the house in the basement. The other line in the basement doesn't have any open branches. Odors are coming from the pvc. How do I correct this?

That is an open, and likely illega,l sewer connection. Can you reroute that line to drain into a laundry sink or floor drain?