If the dishwasher contains parts made of earthenware or porcelain, it cannot be koshered. However, for other types of dishwashers, the process is as follows:

We must first clean it thoroughly, ensuring no food residue remains. One must then refrain from using the dishwasher for a full 24-hour period to ensure that any absorbed flavors become “nullified” (Pagum). Afterward, run the dishwasher through its longest cycle at the highest temperature setting using a strong cleaning agent (Chומר Pogem). Through this process, the body of the dishwasher and the racks are considered koshered for Pesach (Igrot Moshe, Vol. 3, 56).

Regarding plastic trays and racks: According to Rabbi Moshe Feinstein (Igrot Moshe, Vol. 2, 92), plastic cannot be koshered. However, according to the Minchas Yitzchak (Vol. 3, 67), if the vessel will certainly not be ruined by the heat, there is no restriction, and it may be koshered through boiling (Hag’ala). This was also the ruling of the Chelkat Yaakov (Vol. 2, 163).