This design is originally by user @dpolz_208124 from printales.com. The original design is available under the Creative Commons Public Domain License, allowing me to distribute it further. At this point, however, a huge thanks to the designer and for making his project available.
After printing, remove the supports. For example, drill a hole using a stepped drill bit until the refill cap fits into the hole. Secure the cap inside the hole with a compatible adhesive. Optionally, use a seal approximately 19-21mm in diameter on the refill cap plug.
After one good print, I ran into some issues, so I had to edit the print profile.