if something is expelled in a process, then that something is a waste product of that process
digestion is chemical_process. excreting is emission_of_object. refining is process_of_removing_unwanted_material. purification_process is removing_from_stuff. evacuating is excreting. excreting is bodily_function_event. animal_excreting is excreting. purification is purge. vomit is expulsion. purge is removal.