You can use any triangulated object with this emitter. The outside faces of the object will be used to create the particles along the polygons' normals. If the normals point to the inside the object can be filled.
...
Type
Toggle the emitter's type with this drop-down menu. The following parameters and the viewport representation will be updated according to your selection. Bear in mind that type changes will change the emitter's and fluid's behaviour completely.
...