This is from a thread last fall:
Here is the order of steps. Try this in a fresh, layerless, classless file.
1) draw a line
2) select the line and copy it
3) create symbol... - make sure that you select "leave instance in place"
4) right click on the newly made symbol in the resource browser and select "edit... 3D"
5) select "edit - paste in place". The line that you copied in #2) should paste in place.
6) extrude that line.
7) exit the symbol.
8) reselect the symbol on the page.
9) convert it into a lighting position.
10) now everytime you add the symbol as a position - you will be able to give it a z value.
Note that if you are extruding a line for the 3D portion you get nothing but a vertical plane. In order to get a "pipe", you need to draw a circle, extrude it into a pipe, and then reorient it into the proper position - all while working in the 3D part of the symbol's resource.