I have noticed that when exporting a drainage network to DWfx or Navisworks custom contexts assigned to the pipework & Structures are not being displayed.
I have added a calcalated parameter which works out the pipe surround area but this does not show in either format, after noticing this I found that actually all of my custom contexts are not exported. This is causing me some headaches because I have been using the custom contexts to add aditional detail into the Bim Models which were unavaliable before.
I am wondering if this is as designed out of the box or if there is some clever tweak we need to do to get this data to export correctly?
Edit: Also if you append the drawing directly to Navisworks it still does not display the custom information either?
Sorry that I don't have a solution to your problem, but I can verify it. We ran into the same issue a couple of years ago trying to create a BIM deliverable in Navisworks file format. Navisworks only appears to be able to display Civil 3D's default pipe and structure properties. We ended up adding our custom properties to the pipes and structures with a user data tab in the Navisworks properties window. User properties are accessible with the Navisworks API, so some of this can be automated.