The container you are referring to is usually called a mothball holder or a hanging air freshener container. In the context of eliminating cockroaches and insects in the toilet, it works as follows: Function: This container has small holes that allow the smell of the mothball or deodorant block to spread out. Effectiveness: The strong smell of the chemical (often naphthalene or paradichlorobenzene) acts as a repellent that cockroaches and small insects do not like.