In order to reduce any stray vapour charge voltage in the air, the tanks, earth AND fluid need to be at the same potential. ( or as low as possible below flashpoint or LEL).
All fluids are dielectrics and all dielectrics have capacitance. Charge can be created by tribolectric friction of some materials and depleted by fluid transfer (charge transfer). Neglecting the former, I assume;
\$Ic=C\cdot dV/dt+V\cdot dC/dt\$ where dC/dt is the charge depletion rate of fluid flow from some unknown charge Q=CV.
I expect detonation to occur with some threshold above breakdown voltage in air Vth but this threshold gets reduced by Ic from a high dV/dt which is related to current and limited by V/R of the interface.
One usually controls ESD in workplaces by a selected R of 1M to reduce the Ic=V/R for some kV/Megohm where Ic=CdV/dt for a HBM of 100pF and 300pf for a cart with R bonded to earth ground.
Since vapours of combustible gas have a lower explosive limit (LEL) such as H2=4%, this level may be exceeded by some electric field of kV/mm or V/um if the dielectric voltage rises from the above fluid flow effects.
simulate this circuit – Schematic created using CircuitLab
I don't know what OSHA recommends for confined air spaces but one smells explosive fluid in the air in an enclosed space with > 4% H2 , I would make connections with high resitance 1st to neutralize charge then clamp to keep at 0V difference, like ESD wrist and heel straps at low < 1mA current ( 1Meg) then clamp with low R when walking around.