An evaporative emissions (EVAP) system and its method of control comprise commanding a three-way valve to fluidly connect an auxiliary vapor canister and a bottom portion of a fuel tank, controlling at least one of an engine of the vehicle and a purge pump of the EVAP system disposed between the engine, a separate primary vapor canister, and the auxiliary vapor canister to draws fuel vapor from the fuel tank into the auxiliary vapor canister for storage, commanding the three-way valve to fluidly connect the bottom portion of the fuel tank to an atmosphere outside of the EVAP system to generate additional fuel vapor in the fuel tank, commanding the three-way valve to fluidly connect the auxiliary vapor canister to the atmosphere, and controlling at least one of the engine and the purge pump to draw the fuel vapor from the auxiliary vapor canister into the engine.