Gemara

(Rami bar Aba): In Tzipori, R. Yosi enacted that women should talk with each other in the Beis ha'Kisei, so a man will know not to go there.

Berachos 62a (Beraisa - R. Akiva): One does not uncover himself while standing, rather, while sitting.

(Rav Tanchum bar Chanilai): Anyone who is Tzanu'a (modest) in the Beis ha'Kisei is saved from Mazikim;

Some say, even his dreams are not disturbed (by Mazikin).

(Ula): One may relieve himself immediately in back of the fence. In a valley, he should go far enough that no one will hear if he passes gas.

(Isi bar Nasan): In back of the fence, one should (go so far that gas will) not be heard. In a valley, he should not be seen.

(Rav Ashi): Isi meant that what he exposes should not be seen, but he himself may be seen.

(Beraisa): A Tzanu'a is one who eliminates in the same place (i.e. a corner out of people's view; alternatively, in the same way, exposing himself no more) at night as he does during the day.

62b: Rav Safra went to the Beis ha'Kisei. R. Aba snorted outside (to see if someone was inside). Rav Safra said 'Lei'ol Mar' (enter, master)!

R. Aba (after he left): You acted improperly! (You should have snorted back, and I would have known not to enter!)

(Mishnah): In the Mikdash there was a Beis ha'Kisei of honor. One knew when someone was inside, for only then it would be closed.

Rav Safra talked because he feared that if R. Aba would go away, and the delay before eliminating could endanger him!

(Beraisa - R. Shimon ben Gamliel): If feces started to leave and returned to the body, this can cause Hidrokan (swelling of the stomach). If urine started to leave and returned, this can cause jaundice.

Tamid 27b - Rav (to his son Chiya): Sit before you uncover yourself, and cover yourself before getting up.

Rishonim

Rif and Rosh (Berachos 45a and 9:28): We do not uncover while standing, rather, while sitting. Ula permits relieving oneself immediately in back of the fence. In a valley, he goes far enough that no one will hear if he passes gas. Rav Ashi permits where his exposure is not seen.

Rosh: Rav Ashi allows even if the person himself is seen. A Tzanu'a is one who eliminates the same way at night as he does during the day.

Rambam (Hilchos De'os 5:6): A Chacham is very modest, even in the Beis ha'Kisei. He does not uncover himself until he sits. He enters the inner chambers of the cave to eliminate. If he goes in back of the fence, he distances himself so that others will not hear if he passes gas. In a valley, he distances himself so others will not see his exposure. He does not speak when eliminating, even for a great need. He is very modest at night, just like during the day.

Rambam (Hilchos Isurei Bi'ah 22:14): Chachamim enacted that women should talk with each other in the Beis ha'Kisei, so a man will not enter there, due to seclusion.

Hagahos Maimoniyos (3): Rashi (Sanhedrin 19a DH mi'Shum) says that this refers to a Beis ha'Kisei in their days, which was in the field, and everyone went there to eliminate.

Or Zaru'a (137): Modesty and silence in the Beis ha'Kisei save from Mazikim. We do not talk there due to modesty. We did not enact that men talk there, for a woman is not so brazen to enter seclusion with men.

Poskim

Shulchan Aruch (OC 3:2): One must be modest in a Beis ha'Kisei and not expose himself until he sits.

Mishnah Berurah (2): He covers himself before getting up.

Kaf ha'Chayim (2): If one is modest in the Beis ha'Kisei, Ru'ach Ra'ah and death do not rule over him, and this lengthens life. This refers to a bowel movement. One should not be modest about urinating (e.g. delay in order to find a secluded place - PF, based on Bechoros 44b).

Rema: Two men should not go together. One may not speak there. He should close the door in back of himself, for modesty.

Magen Avraham (2): It was enacted that women talk with each other there, to avoid seclusion. We are not concerned in the city.

Machazik Berachah (6, brought in Sha'arei Teshuvah 2): We learn from the case with Rav Safra. Perhaps the Rambam means only when he is actually eliminating, and forbids talking even for a great need, but the Rema discusses the entire time that he is in the Beis ha'Kisei, and when he is not eliminating, he permits speaking when there is a need.

Mishnah Berurah (4): For a great need, perhaps one may talk, but only before eliminating. If he cannot close the door and someone else wants to enter, they snort to each other without speaking. However, for women who go together to a public Beis ha'Kisei, e.g. in the past, in the field, or nowadays in the Chatzer of the Beis ha'Keneses, Chachamim enacted that they talk so men will not enter. It seems that two women enter together.

Kaf ha'Chayim (4): Also women should not go together. One should also train children, so they will be modest and not lewd. This is even for infants. The Gemara forbids a woman to urinate in front of nursing baby.

Kaf ha'Chayim (6): The Ari Zal says that if one talks there, a certain Shed causes him to sin. Soles Blulah says that Chitzonim can cling to words said there, One should think about his finances, lest he think Divrei Torah. On Shabbos, he may think about nice buildings and pictures.

Kaf ha'Chayim (YD 116:113): Sefer Charedim (76b) says that there is danger there due to Shedim, and one is saved only through modesty and silence.

Gra (5): The Rema forbids talking, like Rashi (62b DH u'Veis, who says that the honor of the Beis ha'Kisei was to avoid the need to talk there). Why didn't he explain like in Tamid (that the Kavod was that others would know not to go there)?

Torah Lishmah (24): We learn from the episode with Rav Safra that one may not say even two words unless there is a great need. Also, when one must speak, he may speak normally and need not economize words. (It would have sufficed to say 'enter', without 'Mar'.)

Be'er Heitev (2): All the more so, one may not eat there.

Kaf ha'Chayim (7): At night one may open the door if it is hard to bear the smell and no one will see him.

Shulchan Aruch (85:2): One may say Chulin matters in a Beis ha'Kisei or bathhouse, even if Lashon ha'Kodesh.

Sefer Chasidim (994): A Zaken explained why he lived so long. Even when people talked to him in Lashon ha'Kodesh in the bathhouse, he made a fence and did not talk in the bathhouse or Beis ha'Kisei even Chulin matters, even though it is permitted.

Magen Avraham (2): It is Midas Chasidus to be stringent (about Lashon ha'Kodesh).

Minchas Yitzchak (4:61): Toras Chayim says that the Isur to speak in a Beis ha'Kisei applies also to a bathhouse, lest he come to speak in Lashon ha'Kodesh and say Hash-m's name. The Magen Avraham holds that Sefer Chasidim's Midas Chasidus is not to speak Lashon ha'Kodesh in a bathhouse. The Rambam (Hilchos Kri'as Shema 3:5) permits saying Chulin in Lashon ha'Kodesh there. He forbids only when eliminating. Perhaps Sefer Chasidim is stringent not to speak at all there, like his final words connote. People are not careful not to speak in a Mikveh; Chachamim are not pleased.

Shulchan Aruch (EH 22:13): Chachamim enacted that women talk with each other in the Beis ha'Kisei, lest a man enter and be secluded with them.

Prishah (22): Chachamim were not concerned lest a woman enter where there are two men, for a woman may be secluded with two men, unless they are lewd. The Rambam forbids this. He must explain that the enactment is based on the Mishnah that permits one woman with two men, i.e. men of extraordinary piety (such men are not found today).

Question (Apei Zutra, brought in Hagahos Ma'ase Nisim (1)): Also lewd men can enter a Beis ha'Kisei! According to the Rambam, they should have enacted that also two men talk there! Also, if one is there alone, how can we answer? I do not understand the enactment.

Rema: Some say that this was only in their days, when the Beis ha'Kisei was in the field, but nowadays that it is in the city, we are not concerned.