Supposing you had a cylindrical closed tank inside the body of a submarine; the top of the tank is at 200m depth. The tank has height 2.5m and internal volume 1.8m^3.
A section of pipework is connected between the top surface of the submersible (level with the top of the tank) and to the tank...
Supposing you had a tank mounted to the outside of a submersible vehicle.
The tank lid is left open, and the vessel that taken down to 200m sea water depth, to top of tank.
The tank lid is now closed at this depth; it is assumed that the tank is completely full, with no air gap/bubble on top...
