Yes, you need a 1.5" threaded x barbed connector but I would not include a valve on the overflow, it serves no purpose. When you shut the system off for cleaning or whatever the overflow piping will already be drained and an air gap is stopping any further flow.
You will never ever want to restrict or throttle the overflow since its the return pump that controls the flow not the overflow which just matches the pumps flow so it serves no purpose. Leave it like you had it in your first post with no valve for simplicity.
You will never ever want to restrict or throttle the overflow since its the return pump that controls the flow not the overflow which just matches the pumps flow so it serves no purpose. Leave it like you had it in your first post with no valve for simplicity.