In the label composer for structure labels there is a component named "text for each" (in addition to the normal text, line, block components) Here you can chose a component for labelling the connected pipes, and with this component you get some more labeling properties. One of them id the connected pipe direction.
I have a question, if anyone out there might know, How does C3D decide the order in which it displays the connected pipe information? Example: I would like it to list the incoming pipe inverts in order of their elevation, highest first.