Halachos for Erev Shabbos Kodesh

1) Water is the only acceptable liquid in which to kosher utensils L'Chatchilah, as the nature of boiling water is to expel that which has been absorbed into the utensil, whereas the nature of other liquids is to be reabsorbed into the utensils.

If utensils were koshered in other liquids, they should be re-koshered in water. (See Mishna Berura Siman 451:26)

2) B'dieved, in cases of necessity and when no water is available, other liquids may be used. (See Rama Orach Chaim Siman 452:5 and Mishna Berura S"K 25 and 26. See also  Shu"t Igros Moshe Yoreh Deah Vol. 1 Siman  60 and Vol. 2 Siman 41, Shu"t Shevet Haleivi Vol. 6 Siman 115:4 and Shu"t Melamed L'Hoel Orach Chaim Siman 96)

Halachos for Shabbos Kodesh

1) It is permissible to add soap or other chemicals and cleaning agents to the pot of boiling water being used to kosher utensils. (See Shulchan Aruch Yoreh Deah Siman 95:4. See also Shu"t Chacham Tzvi Siman 101, Shu"t Chasam Sofer Orach Chaim Siman 120, Chazon Ish  Yoreh Deah Siman 23:1 and Orach Chaim Siman 122:6 for more details about this Halacha.)

2) A pot of boiling water that was used to kosher a large volume of utensils to the point that  the water becomes murky (from all the matter that was expunged from all the utensils) should not be used for any additional utensils and a clean batch of water should be boiled up. (See Rama Siman 452:5 and Kitzur Shulchan Aruch Siman 109:14)

If the water isn't changed, the koshering done in the murky waters may be invalid even B'dieved. (See Mishna Berura Siman 452:27)