The Shulhan Aruch, in his presentation of the laws relevant to Ereb Yom Kippur, writes that it is proper for men to immerse in a Mikveh on this day. This marks the only instance in the entire Shulhan Aruch where we find mention of a Halacha involving men’s immersion in a Mikveh.
Different reasons have been offered to explain this custom. Some claim that this immersion serves to purify a man from the impurity caused by "Keri" (semenal emissions), and one should endeavor to begin Yom Kippur in a state of ritual purity. Others explain this immersion as a symbolic expression of our desire and efforts to divest ourselves of our sins. The Torah (Vayikra 16:30) speaks of Yom Kippur as the day on which we are "purified" from our sins. In light of this comparison drawn between atonement and purification, we undergo immersion in a Mikveh as a symbolic expression of our desire to achieve atonement.
The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Nisavim, writes that a man should immerse five times in the Mikveh on Ereb Yom Kippur. During the first immersion, he should have in mind that he seeks purification in a general sense. The second immersion serves to correct the particular flaw of anger; thus, as one goes under the water for the second time, he should have in mind that he seeks to repair all the spiritual damage he caused by growing angry. The third immersion serves to "sweeten," or assuage, the harsh judgments that God might issue against us. Through the fourth immersion, we seek to remove the spiritual "garments" of the weekday, thereby preparing our souls for the awesome, holy day of Yom Kippur. Finally, the fifth immersion serves to bring upon us the sacred "garments" of the soul for Yom Kippur.
Although one must endeavor to immerse in a Mikveh on Ereb Yom Kippur, if he cannot make it to the Mikveh he should instead have nine "Kabin," or approximately 12.5 liters (roughly 3.5 gallons), of water poured over him. Thus, one who cannot go to a Mikveh can stand under the shower for the amount of time it takes for this quantity of water to pour on him. (The Ben Ish Hai mentions a third option, namely, washing one’s hands forty times in a particular sequence, the details of which lie beyond the scope of our discussion.) In any event, as mentioned, it is proper to make an effort to immerse in a Mikveh.
It is preferable to immerse on Ereb Yom Kippur before reciting the Minha prayer. Some have the custom to go to the Mikveh a second time after completing the Se’uda Mafseket (final meal before the fast), in order to ensure that they are pure at the onset of Yom Kippur.
During the time of the Shulhan Aruch, and until recent times, it was customary for women, and even single girls, to immerse in a Mikveh on Ereb Yom Kippur. Nowadays, however, women do not immerse on Ereb Yom Kippur, and certainly single girls should not immerse, as it is customary for single girls not to go to the Mikveh at all until before their wedding.
Summary: It is proper for single men to immerse five times in a Mikveh on Ereb Yom Kippur, preferably before Minha. Some have the practice to go to the Mikveh again after completing the final meal before the fast.
