Final answer:
Without a direct reference to GRAVITY XFLOW switchlight in standard aviation nomenclature, a precise answer can't be given. However, in aircraft, gravity crossfeed typically involves fuel transfer between main tanks for load balancing.
Step-by-step explanation:
The GRAVITY XFLOW switchlight is likely a component specific to aircraft systems, controlling the fuel transfer process. Given the information provided, a direct answer isn't possible as the term GRAVITY XFLOW does not seem to correspond to standard nomenclature used in aviation or any common fuel system control component. However, in aircraft fuel systems, gravity-crossfeed operations typically allow for fuel transfer between main tanks to balance fuel load between wings or engines. If there are only main and center tanks in the aircraft configuration, that would rule out auxiliary and transfer tanks immediately.
In general, switchlights like a gravity-crossfeed or similar component can help manage fuel dispersal across different sections of the aircraft's fuel storage areas, often under the control of the aircraft's fuel management system. The scenario described in the reference information about flow-through involving ballast tanks is more akin to maritime operations than aircraft fuel management, as aviation fuel tanks do not operate on a ballast system.