With the first parts designed, it's time to fire up the 3D printer and crank out the plastic parts. The outlet I mentioned last time with the black hole was indeed a problem. Although it passed all the checks in the FreeCAD Mesh Workbench, the stl had big problems when fed to netfabb. I had to import the stl into OpenSCAD, subtract the center cylinder, and create another stl. This worked fine and the part printed out OK.
Had to change plastic in the middle of printing parts. Not uncommonly, this means a few hours characterizing the plastic and resetting parameters in Slic3r. But I got lucky this time, the new plastic uses the same settings as the old and prints perfectly. Here's a shot of some of the new parts.
Next up is to finish the design of the coupler and the plunger, then put it all together and give it a try.