45:4 The cup used for bentching must be whole. If it broke - even on its base - or if it has any defect in the rim, or if it has a crack, it is not fit for use. (If the only cup available is defective, it is better to use it than to discard the use of a cup altogether – Mishnah Brurah 183:10-11.) The cup for bentching must washed inside and rinsed outside or wiped clean. One pours wine from the bottle into the cup specifically for the sake of performing the mitzvah; the cup should be filled. The one who is to lead bentching should accept the cup with both hands to show how much he cherishes the mitzvah and to parallel Psalms 134:2, “Raise your hands in holiness and bless God.” After accepting the cup with both hands, he removes his left hand so that he is holding the cup in his right hand only, so that he does not make the mitzvah appear to be burdensome. He should look at the cup and not allow his attention to be diverted. The cup should be held a handbreadth above the table (about three and a half inches) in order to parallel Psalms 116:13, “I will raise the cup of salvation and call upon the Name of God.” (The reason the cup is raised is so that the other diners may see it; the Biblical verse is an after-the-fact support for the practice – MB 183:16.) A left-handed person should hold the cup in his strong hand. (An ambidextrous person should use the right hand – MB 183:20.) The empty plates should be removed from the table before bentching.
45:5 If those dining are of equal stature and there is a kohein among them, there is a mitzvah to honor him with leading the zimmun as per Leviticus 21:8, “You shall sanctify him.” (Unlike the first aliyah of Torah-reading, a kohein may decline this honor in favor of a non-kohein – MB 201:13.) However, if there is an especially great or important man among the diners, he should lead. (If one of the diners is the host, the honor is his to distribute to one of his guests – MB 201:1.) The practice is to have a mourner lead bentching if all present are on the same level. The honor of leading should be given to one who is gracious, hates injustice and performs good works with his money. Proverbs 22:9 says that “the gracious person will be blessed” (“blessed” = “yivorach”), which can also be interpreted as “the gracious person will bless” (“will bless” = “yevareich”).