I thought this might make a great video for those who are not familiar with Filters and Visibility Graphic Overrides.
The challenge was to get ’round’ ducts (or pipes) to display their ‘centerlines’ when you switch to ‘hidden line’ visibility because by default the centerlines only show when the view is set to wireframe visibility.
Some say that you should not need to show centerlines but regardless of the camp you are in there is a work around and the lesson learned can be applied to many aspects of REVIT MEP, Architecture or Structure.
Create a ‘filter’ to grab the ’round ducts’ then apply that filter to a plan view and set them to ‘Transparent’.
Source