The bigger the socket and the wrench the more torque you will be able to apply. If it has not been removed in some time you might want to take a wire brush to the threads on the outside of the rod as close to the tank as possible clean them and spray them with some kind of good penetrating fluid. WD 40 is ok...but there are better choices.
Hope that helps.
Glen & Robyn (A.K.A. Puff & Crickit) Full Timers..
2006 F350 6.0 with 3.73 gears, 4X4, Extra-Cab Long Box, Oil/Tranny/P.S. Coolers. Coolant filter. SCT Livewire.
2011 Cedar Creek 36RE, Auto levelers + too much to list..!