Halacha requires that when one purchases or receives a utensil from a gentile, he must immerse the utensil in a Mikveh before is allowed to use it.
The question was asked as to whether this Halacha would require a convert to immerse all his utensils upon converting. Once a gentile undergoes conversion he becomes fully obligated in all Torah laws, and hence he may not use utensils that had been owned by a gentile until he immerses them. Since his utensils had belonged to a gentile himself, before conversion it would appear, at first glance, that Halacha would require him to immerse all his utensils, just as one must immerse any utensil acquired from a gentile.
Chacham Ovadia Yosef addresses this question in his work Yabi'a Omer (vol. 7, siman 8) and rules that a convert is not, in fact, required to immerse his utensils after conversion, and he bases this ruling on two arguments. Firstly, a famous Halachic principle states, "Ger She'nitgayer Ke'katan She'nolad Damei" "A convert who converts is similar to a newborn child." The process of conversion is treated by Halacha as if the individual is reborn, such that all prior relationships with people and objects are annulled. Hence, from the standpoint of Halacha, a convert's possessions become legally ownerless "Hefker" as a result of his conversion. As such, when he returns home from his conversion, he takes possession of his utensils anew. Since the obligation to immerse utensils applies only to utensils acquired from a gentile, and not to utensils taken from "Hefker," a convert is not required to immerse his utensils after his conversion.
Chacham Ovadia then cites another argument in the name of the Avnei Neizer (classic work of responsa by Rabbi Avraham Borenstein of Sochatchov, Poland, 1839-1910), who posited a novel theory with regard to conversion. The conversion process consists of a number of stages, including the convert's immersion in a Mikveh. The Avnei Neizer contended that the convert's immersion of his body effectively functions as an act of immersion for all his possessions. Although only he immerses, his immersion suffices for all his belongings, as well. Therefore, a convert may use his utensils after conversion without immersing them, as they are considered to have been immersed along with him.
Summary: Although generally a utensil acquired from a gentile must be immersed before it may be used, a convert is not required to immerse his utensils after his conversion.
