Was there really a shuttle toilet training device with a camera looking up at the user's fundament? This seems a bit undignified to say the least.
Yes, this was the Waste Collection System (WCS) Positional Trainer, located in Building 5 at Johnson Space Center, adjacent to but not part of the Shuttle Mission Simulator Fixed and Motion Bases.
The trainer was located in a small room with a code-locked door. The room contained a conventional toilet, a functional replica of the shuttle toilet, and the WCS Positional Trainer. (The conventional toilet was behind the gray door to the left of the image).
Due to the small size of the seat opening in the shuttle toilet and the necessity to achieve a positive seal between the user and the seat so that the airflow worked properly, correct positioning of the user on the seat was critical.
The WCS Positional Trainer had a camera and light in the seat as shown below.
The image from the video camera was displayed on the monitor in front of the user. A placard on the wall gave instructions for use.
This room was a highlight of any informal tour of the training facilities.
Personal photos except photo of seat is a screenshot from the video below, which I recommend watching for more information.