Then under �meshes� rollout create a new mesh. Right click it an insert our fluid. If you have a dense particle system, choose a small radius, otherwise make it a bit larger to make it seem like a liquid. You can also change its detail by making the polygon size smaller (more faces) or larger (less faces).
Open the �export central� menu and check both the emitter and the mesh to be exported. All you have left to do now is press the �action� button (with lock animation off) and wait and wait until the juice fills the glass.
Back to 3dsmax, import the mesh to the keyframe you wish, by using the Real Flow mesh loader.