Soo I have this sphere which is used as a source volume and it fills up the sphere with particles. I activated the display of the particle fluid surface and played a bit with the settings, but I can't get the part that is in contact with the sphere to be smooth.
For all also wondering how this was achieved: I believe he basically cuts away a part of the liquid via this RAY-node and then smooths it again. This results in a very clean surface