Cloning pool

A cloning pool was cloning technology used by the Sontarans. During the Sontaran invasion of Earth, Martha Jones of UNIT was cloned, her copy made in 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 in the back of the neck. When Martha Jones was cloned, her clone reached out and pulled the umbilical cord free from the back of her neck. (TV: The Sontaran Stratagem / The Poison Sky)

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