How much energy is needed to empty a 1m3 tank filled water under 10m of water?

Energy is not a physical unit. It is a philosophical concept and an accounting technique used to analyze mechanical and chemical exchanges. In nuclear physics it is defined as a color of light, in biology it is a synonym for metabolism, and in public utilities they say energy when they mean connectivity.

Moving water involves work or power. To find work, you need to specify how high the tank is and to what height you want to move it. To find power, you also need to specify the time it takes.