An engineer might be better to explain this, Jojo, but as from context, it seems to be related to the run and rise of an angle. In this case, the speaker is referring to “run” of the pipe, from which you can infer they mean length of the pipe, or the installation along the length of the tubing.

The run of tubing is the placement of the tubing. Another example, the road ran along the river, which means the road was along the river, or 'followed' the route of the river. In a house or building, the wiring diagram will show where the wires will run in the house or building.

It means the laying and placement and the route of the tubing and the total length. Either for the whole job or each section of the job. If you were to run (lay) pipes around the edge of this comment box. The total run would be two times the height (depth) and two times the depth (the width) in pixels. 1) carefully measure before cutting double check first before cutting the four tubing runs (each piece of tubing) 2)Ensure that you design where the connections are located and that easy removal can be achieved later if required for maintenance or in emergencies. 3) do not run any tubing (position place fix) low down towards the floor in such a position that people would be naturally inclined to use the tubing as a 'foot rest'. Likewise, it can be dangerous to attach the tubing to a higher position that people would be naturally inclined to use as a handrail, or towel rail etc in a bathroom. bus rail is possibly an American term that would mean the same sort of thing you do not want people to use the tubing for anything. Bus rail seems to mean the distance between bus stops. (from google searching). so you do not want people to instinctively​ grasp hold onto the rail to steady themselves at certain intervals as they walk around the edge of the comment box.