One embodiment of the method includes: closing both the inlet valve and the outlet valve, connecting a cryogenic liquid source to the cryogenic liquid inlet conduit, and introducing cryogenic liquid into the cryogenic liquid inlet conduit; opening both the inlet valve and outlet valve, thereby introducing cryogenic liquid into the sampler vessel inner volume, the cryogenic liquid has a free surface; closing both the inlet valve and the outlet valve after cryogenic liquid flows from the purge tube; disconnecting the cryogenic liquid source from the cryogenic liquid inlet conduit; opening the inlet valve, thereby allowing cryogenic liquid to flow from the cryogenic liquid inlet conduit; and closing the inlet valve after the free surface in the sampler vessel inner volume drops below the top of the first cryogenic liquid level, and the cryogenic liquid flow stops.