Bio Tank is a kind of building for Epsilon Army to store the Libra Clones or some creatures used for research or for weaponization. It have 3 small types and a large type.
The first of Bio Tank appear in the Soviet mission Exist to Exit. This Bio Tank will explode after a period of time in the game. According to the briefings after this mission, there might be a Libra Clone in it.
There are 4 Bio Tanks in the main base of Epsilon Army in each Allied missions Hysteria and Relentless. Their use are unknown in the mission, they might just for storing some normal weaponized creatures.
There are 4 abandoned and empty Bio Tanks in the Soviet co-op mission Intoxicated. After Reznov and Krukov find them, both colonels will associate to another one appeared in the mission Exist to Exit.
In the missions Insomnia and Unthinkable, the Allied Army destroyed many of Bio Tanks in the Epsilon base.
In the Soviet mission Earthrise, there are amount of damaged and empty Bio Tanks landed on the right side of the map, one of them is a large type.
24 Bio Tanks appear in the Allied mission Parasomnia. To destroy them and to capture the Libra Clones exit from them by the Chrono Prison is the order of the secondary object.