Filled Pipes for Cyberman

I had trouble printing the pipes for the Cyberman head because the vertical (when mounted) sections are hollow. I filled the pipes using OpenSCAD but couldn't get it to render both models together so I had to go through the following process:

1. Line everything up in OpenSCAD but only render my "pipe filler" parts of the model. Export as STL.

2. Open the original STL in Meshlab. Open my "pipe filler" STL as another layer.

3. Select Filters --> Layer and Attribute Management --> Flatt