The Central Specimen Tank appears in the Metroid Processing room in Metroid Prime 3: Corruption. Samus finds that its lift is stuck when she enters the room. This can be fixed when she enters the basement and repairs a broken Circuit board. It will then open up a Morph Ball hole, which Samus can enter. The lift will take her to a balcony, where she can continue exploration.
Visually, the Central Specimen Tank resembles the Kellium energy reactor from Metroid Prime 2: Echoes, in the Main Reactor room where Dark Samus is fought for the first time. Both tanks appear in the middle of the room, are very hardy and contain a lump of crystallized Phazon.
"Central Specimen Tank. Capable of moving between floors. Unit is receiving insufficient power."
"Central Specimen Tank
Power restored and auto-cycling between floors."