Q. Dear Rabbi, If someone owns a rental property and a Gentile tenant returns his unit during Pesach, and it contains a sizable amount of abandoned chometz, what should he do? How should he clean it for the next tenant?
A. Horav Shlomo Miller's Shlit"a opinion is to rent out to a Gentile, in the Mechiras Chometz process, the complete rental facility for the Pesach period. This is necessary even though the chometz does not belong to the landlord, as he never had the intention to acquire it. However the departing tenant could have been Jewish and the remaining chometz, could be considered "chomtzoi shel Isroel birshus Isroel", or chometz that is owned by a Jew and is now in the property of the Jewish landlord. This is prohibited according to the Gr"a, Beis Meir and other authorities. The landlord should also instruct the superintendent or a gentile worker beforehand to clean and prepare the unit when the tenant returns it. Although he rented out the entire facility, it is understood in the agreement that he can still enter it and do what is necessary for its upkeep, as he is to return to it shortly.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a.