An assembly including a holder and a fluid-fillable container. The holder is adapted for holding at least the container and includes a system for filling the container with a fluid from a fluid source. The holder further includes a detector for detecting the fluid level inside the container, a light source for at least locally illuminating the interior of the container and an optical detector. The detector is arranged outside the container and for detecting a fluid level inside the container by detecting light scattered inside the container resulting from the light emitted by the light source.