It has become customary to rinse the vessels in cold water after the immersion in boiling water, to avoid the vessel reabsorbing the boiling water that was now mixed with the chametz discharges of the vessel. Even though these have been nullified and are less than one in sixty of the volume, people still ideally rinse it in cold water, as prescribed by the Shulchan Aruch of our great master Zalman [Shneur Zalman of Liadi] of blessed memory, and the Levush gave a different explanation for this practice.