I missed your last reply - are you still dealing with this issue? If so - (1) do you want the Voronoi to have it’s internal struts, or do you want only the ones that form the top, bottom, and sides of the cylinder, and (2) why do you want to convert the results to a mesh? If you want to smooth out the pipe connection you can try using Multipipe instead of just Pipe.
For 3D printing most people (including me) end up with one or more Closed Breps, and then export these as an STL file. Converting to a mesh before exporting runs the risk of introducing errors into the final result and these can be difficult to resolve.
Also - take a look at this message thread - it is almost exactly the same as your original question:
https://discourse.mcneel.com/t/merging-3d-voronoi-network-into-one-unified-object/118672