Is there a way I can find all items in the containment tree that are not used in any diagram? This would be useful to tidy up models.
You can easily find elements that are not used in any diagram using MagicDraw Find functionality.
Select command Find... from the main Edit menu to invoke Find dialog. Then specify search scope (we do not recommend to search in the whole Data package, as elements from modules will be found), and select checkboxes "Search data unused in diagrams" and "Load diagrams and unloadable modules".
Elements that are not used in any diagram will be displayed in the Search tab in model browser.