Gemara

8b (Rav): If one slaughtered with a Nochri's knife, he must peel off a layer from the areas cut;

(Rabah bar bar Chanah): It suffices to rinse them.

Suggestion: They argue whether Beis ha'Shechitah (the place of slaughter) is Rose'ach (hot enough to be Mavli'a, i.e. cause absorbed taste in a knife to enter the meat).

Rejection #1: No. All agree that it is Rose'ach. Rabah says that it suffices to rinse. Since the Simanim are busy exuding blood, they are unable to absorb tastes exuding from the knife.

Rejection #2: No. All agree that it is not Rose'ach. Rav obligates peeling off a layer. The sharpness of the knife causes its absorbed tastes to enter the meat.

(Ameimar): One should not fold (the place where the Chelev of the kidney is in) a flank of meat onto the meat, for the Chelev will flow and be absorbed by the meat.

133a (R. Aba): If a Kohen does not know to remove the veins in the jaw (they are full of blood), we do not give to him the jaw.

Rejection: We give to him. He will not eat forbidden blood!

If he roasts the jaw, the blood will flow out. If he cooks it, the blood will come out when he cuts the veins and salts the meat!

134b (Beraisa): In a place where people are Moleg calves (pour boiling water over them, and eat them with the skin) one must give the Zero'a to the Kohen in its skin.

Zevachim 95b (Beraisa): "Asher Tevushal Bo" teaches about a pot in which Chatas was cooked (it must be broken if it is earthenware, or Kashered (Merikah u'Shtifah) if it is of metal).

Question: What is the source for a pot into which boiling Chatas was poured?

Answer: We learn from "Asher... Bo Yishaver" - if it absorbed Chatas (in any way).

Rishonim

Rif and Rosh (Pesachim 8b and 2:7): Kelim used for Chametz in a Kli Sheni, e.g. bowls, it suffices to pour boiling water on them in a Kli Sheni and wait until the Isur is purged. We learn from pots of Nochrim. Everything is Kashered the way it is used.

Rambam (Hilchos Chametz 5:24): If Kelim of metal, stone or wood were used with Chametz in a Kli Sheni, e.g. cups and bowls, he puts them in a big Kli and pours boiling water over them and leaves them there until they emit (all absorbed taste). Then he rinses them, and he may use them for Matzah.

Rambam (Hilchos Ma'achalos Asuros 7:19): A butcher may not spread Chelev of the flanks on the meat to beautify it, for the membrane over the Chelev is thin, and it will be crushed and the Chelev will flow and be absorbed in the meat. If this was done, the meat is not forbidden.

Mordechai (Avodah Zarah 858): If chickens were Nimlegu together in a Kli Sheni, and one was found to be Tereifah, the Ri says that this often happens and we permit the rest, for a Kli Sheni does not cook, emit or absorb. He brings a proof from the Yerushalmi. However, R. Chaim Kohen says that this is no less than Beis ha'Shechitah and a knife used for slaughter, which must be Kashered. This shows that even though it does not cook, it is Mavli'a. If so, all the Kelim used for Meligah are forbidden due to blood that the chickens emit and the Kli absorbs. The other chickens are permitted, for whatever blood they absorb will leave through salting. The Ri permits even if they did not wash the neck, and did Meligah when it was dirty with blood. The custom to wash the neck is because the water is used for Meligah of other chickens, or to rinse the Kelim. Avi ha'Ezri says that it does not cook, but it emits and absorbs. If a Kosher chicken was Nimlag with a Tereifah, it is forbidden, for the fat of the Tereifah disperses through the water and is absorbed (in the Kosher chicken) more than blood (Chulin 112b). It is forbidden even if the Kli has holes. This is unlike Meligah of Kosher chickens together. However, even water of Meligah of Kosher chickens should not be boiled for another Meligah or to rinse pots, for the absorbed blood will forbid them.

Rashba (1:844): If a chicken was Nimlag in a Kli Sheni that is Yad Soledes Bo, even though it emits blood and absorbs it again, the blood will come out through salting or roasting. However, if the chicken was salted and delayed the proper time, but not rinsed, and put in a Kli Sheni that is Yad Soledes Bo, the blood is reabsorbed but will not come out through salting or roasting.

Beis Yosef (DH veha'Rashba): The Rashba says that even if we consider Iruy like a Kli Sheni, it is forbidden. This implies that even after pouring into the Kli Sheni, one may not put in (meat), for even though a Kli Sheni does not cook, it emits and is Mavli'a. He proved that a Kli Sheni is no worse than Beis ha'Shechitah or the flanks shortly after Shechitah. Chachamim forbade putting them on meat, lest the Chelev flow and be absorbed in the meat. Therefore, Meligah is permitted only after salting and removing the Chelev.

Beis Yosef (ibid.): This implies that Meligah even of fowl is forbidden, even in a Kli Sheni. Even though it has no Chelev, blood is emitted from one limb and absorbed in another. He holds that blood absorbed in this way never leaves through salting.

Ran (31b DH v'Chasvu): Meligah of animals in a Kli Rishon is forbidden in a Kli Rishon, due to Chelev and blood. In some places, they permit Meligah of kids (Chulin 134b). This is after salting and removing the Chelev and Gid ha'Nasheh. Alternatively, it is in a Kli Sheni. However, even though a Kli Sheni does not cook, one should be concerned lest it causes Chelev to be absorbed. Absorptions do not depend on cooking. The heat of Beis ha'Shechitah is less than that of a Kli Sheni, and even so it is Mavli'a (Chulin 8b). However, we need not be concerned for blood. A Kli Sheni is Mavli'a, but not so deeply that it will not come out through salting.

Poskim

Shulchan Aruch (YD 68:11): Some say not to do Meligah even in a Kli Sheni. If he did, it is permitted.

Rema: We hold that a Kli Sheni does not cook, even if it is Yad Soledes Bo. It is permitted b'Di'eved, but forbidden l'Chatchilah. Therefore, one should do Meligah only after salting. However, to honor guests of for needs of Shabbos, one may put in a Kli Sheni a piece full of frost to hasten salting. L'Chatchilah, it is good to put only in water that is not Yad Soledes Bo. We do not distinguish between Kli Cheres, copper or other Kelim regarding a Kli Sheni.

Beis Yosef (DH ul'Inyan): Since the Rashba holds that a Kli Sheni emits and absorbs, one should be careful l'Chatchilah. B'Di'eved, we do not forbid, for the Rambam permits b'Di'eved when the Chelev is still warm.

Taz (6): This is unlike YD 105:2. Here, the Isur is due only to cooking. (There, absorptions alone forbid.)

Shach (27): Toras Chatas (Reish 33) says in the name of the Beis Yosef that the Rashba holds that a Kli Sheni emits and absorbs, but b'Di'eved it is permitted. This is wrong. The Beis Yosef says that b'Di'eved we rely on the Rambam, but the Rashba himself forbids.

Yad Avraham: The Rashba explicitly says in a Teshuvah that the chicken is permitted, for the blood reabsorbed will come out through salting or roasting! This connotes it is permitted l'Chatchilah. Toras Chatas cited the Rashba, i.e. Tosafist R. Shimshon b'R. Avraham (cited in Teshuvos Maimoniyos Ma'achalos Asuros 4), not R. Shlomo ben Aderes (the author of the above Teshuvah, and Toras ha'Bayis). The above Teshuvah (843-844) cites R. Shimshon b'R. Avraham!

Shach (28): The Rema says that a Kli Sheni does not cook, i.e. and also it does not emit or absorb.

Shach (29,30): It is forbidden l'Chatchilah only if it is Yad Soledes Bo. The Heter for guests of for needs of Shabbos is even if it is Yad Soledes Bo.

Shach (33): The Yerushalmi brings an argument about whether or not a Kli Sheni cooks, but all agree that it is Mavli'a.

Gra (31): In Avodah Zarah we require Hag'alah for Kelim of Nochrim used for hot, i.e. even a Kli Sheni. If a bowl was used to salt meat, one may not use it with hot food (Chulin 111b), even though regarding Shabbos salting is not considered cooking.

Gra (32): The Yerushalmi asked incredulously 'do you hold that a Kli Cheres (a Kli Sheni) absorbs?!' Zevachim 95b connotes that only Iruy Kli Rishon is Mavli'a (but a Kli Sheni is not). According to the Rif's text in Chulin, we must say that we discuss Meligah in a Kli Sheni. (I do not see why this depends on the Rif's text - PF.) Even though Toras ha'Bayis says that we could say that it is in a Kli Rishon after removing the veins, Chulin 133a refutes this. (It says that we give Matanos Kehunah before removing the veins.)

Gra (35): The Yerushalmi thought to distinguish between Kli Cheres and copper Kelim, i.e. a Kli Cheres absorbs even if it is a Kli Sheni, but we need not say so in the conclusion, for we discuss Iruy.

Gilyon Maharsha: If there is vinegar or another sharp food inside, even a Kli Sheni cooks (Shach 69:38). If a (meaty) bowl was rinsed with a dairy Kli, we do not say that since this was in a Kli Sheni, it is permitted. The repetition of Iruy is Mavli'a (Taz 95:12). If a Kli Sheni was Yad Soledes Bo, the Pri Chodosh (18) forbids, for it emits and absorbs. The Taz (105:5) forbids, unless it is a big loss. The Shach (105:5) forbids a Kli Cheres that was a Kli Sheni if it is not a big loss.

Kaf ha'Chayim (47): B'Di'eved it is permitted, i.e. the chicken. One can Kasher the bowl, so this is considered l'Chatchilah. If the bowl is of Cheres, which cannot be Kashered, so this is like b'Di'eved, and it is permitted. However, some forbid even a Kli Cheres. Therefore, one should be stringent not to use the Kli Cheres for 24 hours. (After this, all absorptions are detrimental, and do not forbid.)