The toilet of the Self-Contained campervans is easy to remove.
Push the white tab, that is screwed into the floor of the campervan in front of the toilet, so it moves partially forward.
Then push the other corner of that plastic tab so it moves forward fully and the toilet base unlocks.
Then take the toilet base with both hands and move it towards you.
Check out the video below for a demonstration of how to do this...
If that doesn't work, the next best option is to wrap your arms around the toilet as close to the bottom as you can and pull hard towards you. Then it should essentially shunt the clip forward.
See for detailed info and how to use your Self-Contained Spaceships campervan