Flying drones in a tank is not so obvious, there are several factors that make flying somewhat difficult. In a tank there is usually no GPS reception where by the drone will not hold its position, the internal compass of the drone gets interference when flying close to metal structures.

The solution to this is the Elios drone from Flyabilty, this drone is specially designed to fly in enclosed dark spaces.

Internal inspection of a storage tank at Ineos Tessenderlo using a conventional drone.