Add a major system Junction node at the exit of the sag area.

Drag and drop Outfall node from the Tool Box to the Map canvas. The mouse cursor changes to the Edit mode.

Click after the exit of the sag area on the flow path to add a Outfall Node.

Drag and drop Conduit link from the Tool Box to the Map canvas. The mouse cursor changes to the Edit mode.

Add a Conduit link from Storage Unit node to major system Junction node at the sag exit and from the major system Junction node at the sag exit to the Outfall node.