Cloning pool

A cloning pool was a method of cloning utilised by the Sontarans. During the Sontaran invasion of Earth, Martha Jones of UNIT was cloned, her copy was made within a cloning pool.

A cover was kept on the pool during the early stages of cloning. The pool was filled with a dark green liquid, possibly a form of clone feed, which the clone breathed. The pool was connected to a console that held a person as their thoughts were copied into the clone which received them via an umbilical cord. (DW: The Sontaran Stratagem/The Poison Sky)

Nearly the same method is used to create gangers from Flesh. (DW: The Rebel Flesh / The Almost People )