Guys, I need to know how the spare coolant in the gk76a transfer coolant to radiator? By gravity or vacuum? Cos it's getting in my way to swap a gsxr600 tail. I intend to reduce and relocate. Thanks in advance.

All coolant should return from the expansion tank by vacuum.
It is expelled by expansion opening a valve on the cap and is sucked back as the fluid cools in the rad.
As long as sufficient coolant covers the inlet/outlet of the expansion tank and the pipe is well fixed it will
overcome gravity (within reason)

thank you!