Hi Maarten,
for your fuel pump check this Link....
Reinigung des Tankwertgebers beim E32
It is just clipped in, you have to "Squeeze" two little Plastic things, that lie opposite to each other in the mounting frame of the fuel pump, then you can take it out.
You have to remove the fuel level sender.
It should be enough to push onto the pump to take it back again into the right position hearing a click.
There is a cable clip/binder for beeing secure that the pump stays in the mounting frame. Maybe the binder got lost and the pump is out.