The Third Assistant Engineer, also known as the Fourth Engineer, is a licensed member of the engineering department on a merchant vessel. Generally the most junior marine engineer of the ship, this person is usually responsible for electrical, sewage treatment (resulting in the pejorative pun "turd engineer"), lube oil, bilge, and oily water separation systems. Depending on usage, they are called "the Third" or "the Fourth" and usually stands a watch and sometimes assists the third mate in maintaining proper operation of the lifeboats.