Similar to the cable window there is a window for tubes. It is reached via the menu Tubes| Edit. It is easier because there is only one type of tubes. Tubes match the tube type bars, but they are considered as separate objects. For example, I can modify a tube type bar to cable type bar and the bar does not disappear but the tube does.
For comments on the use of this window, see the aforementioned menu Tubes| Edit.
To update the database of the tubes that can be used see section Introduction | Objects | Tubes.