To Reconcile with Your Friend on Erev Yom Kippur, 4 Seifim:Transgressions between people are not subject to atonement on Yom Kippur unless the offender appeases the offended party. Even if one aggrieved another with words alone, this appeasement is necessary. If one cannot effect appeasement at first, one must return a second and a third time, taking along three people each time. If the offended party will not be appeased after three visits, one may desist. RAMA: afterwards, however, the offender should relate before ten people that forgiveness was sought (Mordechai on Yoma, and Maharil). If he is one's Rabbi, one must go to him several times until the Rabbi is appeased. RAMA: one should not be cruel and withhold forgiveness (Maharil), unless it is for the benefit of the one seeking forgiveness (Gemara Yoma). If one was a victim of slander, one need not forgive. (Mordechai and Smag and Hagahot Maimuni, Teshuvah chapter 2, and Mahariv).
2. If the person against whom he sinned has died, then he brings 10 people with him to stand by his grave and he says: "I have sinned before the G-d of Israel and against So-and-So I have transgressed." RAMA: And our custom is to request forgiveness on the eve of Yom Kippur (Mordechai, and Gemara Yoma).
3. The early sages enacted a prohibition and a Cherem (ban) so as not to slander a deceased person.
4. One may immerse and receive lashes whenever he wants, as long as it is before night time, and we do not make a blessing on the immersion. RAMA: One need only immerse one time without (saying) Vidui (the confessional prayer) from an emission. The law of throwing 9 Kabin of water is also from here (Mahariv, Kol Bo, Tashbetz). He who has a loved one die between Rosh Hashanah and Yom Kippur is permitted to wash and immerse on Erev Yom Kippur, as Yom Kippur terminates Shivah (Maharil). This is so even though it is customary to not wash during all of the 30 days; the immersion for a mitzvah is permitted (Da'at Atzmo).