A Jew is forbidden to own chametz on Passover, and our Sages add that when chametz is in the possession of a Jew during Passover, it will remain prohibited even for benefit, even after the holiday. This prohibition only takes effect if the chametz belongs to a Jew. But if this chametz is in the possession of a non-jew, there will be no prohibition to keep it at home during the Passover holiday. Thus, it is customary to sell one's chametz to a non-jew before the holiday (through a Rabbi). Since the sale of chametz is a full-fledged sale, from Torah's perspective, one may even sell "chametz gamur" - "in its entirety".
This sale will include utensils used throughout the year, if it is possible that chametz may have remained attached to them. Although these utensils belonged to a non-Jew during the holiday, it will not be necessary to immerse them in a mikvah once retrieved after the holiday. As for utensils clean of any chametz, it will suffice to hide them in a closed place to avoid using them during the holiday, even inadvertently.
All the chametz and chametz utensils should be gathered in a defined place in the house, which should be well closed before writing on it "sold to a non-jew".
Reprinted from Shoneh Halachot, The Halachic Institute
