Mayim Aharonim

Must I wash mayim aharonim before I say birkath hamazon?

Yes, one should wash with a cup as one does before eating bread. Upon washing one’s hands before mayim aharonim one should say the bracha “asher kideshanu be’ mitzvotav vetzivanu al rechitzath yadayim”, which is in accordance with the opinion of the Raavad, who mentions this view in the name of ancient geonic sources. It seems very likely that the Raavad’s view reflects the practice that was current in Eretz Yisrael.