When the search is completed, one should immediately declare null any chametz which may, unknown to him, still be in his possession. The text of the declaration is as follows:
Any chametz which is in my possession, which I have not seen or disposed of, or which I am not aware of, shall be nullified and ownerless like the dust of the earth.
This declaration is traditionally made in Aramaic. However, if one does not understand the meaning of the words, he may make the declaration in any language which he understands.
A person conducting the search on behalf of someone else should make the declaration in the third person: Any chametz which is in the possession of [the name of the person who appointed him as an agent to conduct the search]. If a woman conducts the search on behalf of her husband, she should say, "in my husband's possession."
The third person form is employed since the people conducting the search are only acting as agents of the owner in fulfilling the mitzvah.
The chametz itself remains the property of the person who owns it, and it is he who will transgress the prohibitions of not seeing or having chametz if it remains in his possession after the time set for its disposal.
It is preferable that the owner himself declare his chametz nullified, for there are those who hold that one's chametz cannot be nullified by an agent.
Any chametz discovered during the search, or which was left to be consumed at breakfast, should be kept in a secure place so that it is not scattered by small children or by mice. It should be burned by the fifth hour of the following day.
When we refer to the fifth hour, we are not referring to 5:00 A.M. The clock according to which all laws are performed is based on the premise that every day has twelve hours and every night has twelve hours. These hours are referred to as seasonal hours and are not based on an hour of sixty, fixed minutes. Rather, the day is divided by twelve and, depending upon the season, the halachic hour will have either more than sixty minutes or less. Twelve of these hours make up the day.
Since the length of the hours of the day and night change constantly, one should consult a calendar or table prepared especially for this purpose [and which lists the time for burning the chametz], rather than relying on one's own calculations.
Although one declares his chametz nullified and ownerless after completing the search in the evening, the declaration is repeated when he burns the chametz the next morning.
The declaration in the evening refers to chametz of which he is not aware; however, a certain amount of chametz was specifically set aside for use at breakfast and was specifically not included in the declaration.
It is possible that some of this chametz may have inadvertently been removed from the place where it was stored, and he may discover it only on Passover. He would thus be culpable for having transgressed he prohibitions of not seeing or having chametz in his possession.
He therefore repeats the declaration and once again renders his chametz nullified and ownerless. The declaration made in the morning differs lightly from that made the previous evening:
Any chametz which is in my possession, which I have seen and which 1 have not seen, which I have disposed of and which I have not disposed of, shall be nullified and ownerless like the dust of the earth.
The change in the text is based on the fact that, in the morning, he intends to render ownerless all of the chametz in his possession, whereas at night, a certain amount of chametz had been left in his possession for use the next morning.
The chametz should be burned before the declaration is made so hat one can fulfill the mitzvah of disposing the chametz while it is still his.
If one forgot to search, or if extenuating circumstances prevented him from doing so, and he did not nullify the chametz before the sixth hour of the morning of the fourteenth of Nissan, he should search for it and dispose of it immediately.
The declaration, however, is not made. Since one may not derive any benefit from chametz after the sixth hour, the chametz is no longer considered to be his, and one cannot renounce ownership of something which he does not possess.
One should carefully rinse his mouth out after finishing the last chametz on the morning of the fourteenth.