Backflow preventer inonyanya kushandiswa kugovera mvura kubva kumadhorobha kuenda kune general sewage unit inodzikamisa pombi yekumanikidza kuitira kuti kuyerera kwemvura kungova nzira imwe chete. Basa rayo nderekudzivirira kuyerera kwepombi yepakati kana chero mamiriro siphon inoyerera ichidzoka, kuitira kudzivirira backflow kusvibiswa.