Siman 12

The sages taught in the Mishnah [41a]: One may not slaughter into a pit at all, but one may make a pit inside his house so that the blood will enter into it; however, in the marketplace one may not do so, so that he does not imitate the Sadducees. Thus far its words. The explanation of the matter is that in the days of the sages of the Shas, there were Sadducees and heretics, and their worship was to carve a pit in a courtyard or in the street and to slaughter into the pit, gathering the blood there and eating over it. Therefore, one who slaughters into a pit appears to be strengthening their worship, even if he does not intend to do so. The sages forbade this entirely, even in a pit that is inside the house, even though the worshippers were not accustomed to performing their worship in a pit in a house.

And one who does not want to soil his house or his courtyard, because he is meticulous regarding cleanliness, makes a pit and makes a place to slaughter outside of the pit and slaughters there, and the blood flows and descends into the pit, for then it is evident to all that his intention is to clean his house and his courtyard and they will not suspect him. However, in the marketplace, even in such a manner it is forbidden, because he is not concerned with the cleanliness of the marketplace [Tur] and it will lead to suspicion. And even though we hold [Shabbat 64b] that anywhere the sages forbade due to appearances, it is forbidden even in the innermost chambers, this is when there is suspicion in the innermost chambers if they were to see; this is not the case here, as there is no suspicion in his house or his courtyard even if they were to see, for everyone knows that he does so for the sake of cleanliness [Tosafot].

And since the sages only permitted it when one makes a place outside the pit, one may infer that even in a pit that is not clean it is forbidden [Semag and Mordechai]. For if it were not so, why would they require such an exertion? They should have permitted it by throwing earth and pebbles into it, as with the water in the previous siman. Rather, it is certain that even in such a case it is forbidden. And even though the service of the Sadducees appears to have been specifically in a clean pit, for they ate over it as has been written, nevertheless they forbade it even in one that is not clean, because not everyone looks inside it to see if it is clean or not. And since the primary prohibition is due to the reason of suspicion, it follows that one must forbid it in every case. Therefore, one who slaughters a wild animal or a bird that requires kisuy must be careful not to dig a bit of earth and slaughter into the excavation and cover it with the excavated earth, for it will appear like one who slaughters into a pit. Rather, he should fill it with earth and slaughter so that it will not appear as a pit [ibid.].

The Tur wrote that the Rambam wrote [Chapter 2, Halacha 6] that if one slaughtered into a pit, it is forbidden to eat from his slaughtering until they investigate after him, lest he be a min. And the Rashba wrote: even though it is forbidden to do so, his slaughtering is not disqualified, for we do not remove a person from his status of fitness until he is investigated and found suspect. Thus far his words. And that which we learned in the Baraita, "he requires investigation after him," this refers to the future; and if it is found that he is a min, we shall forbid his slaughtering retroactively [Rashal and Shach and Bach, and also the opinion of Rashi is so, see there]. And such is the law regarding one who slaughters to seas and rivers in the previous siman [ibid.]. And there is one who says that retroactively it is never forbidden, and also only regarding a pit is investigation required, and not regarding the laws in the previous siman, because there it is actual idol worship and Israel are not suspected of such; but regarding a pit, it is only an act of sorcery, for they would divine in this manner to know future events like the practice of ov and yidoni, and there are those whose desire to know the future leads them to be suspected of this. Therefore, he requires investigation, and it follows that even if he is found suspect in this, one should not forbid his slaughtering for the past, and only for the future they should not allow him to slaughter, for this is not actual idol worship but rather a practice of fools which the Torah forbade [Kereti U-Peleti].

Our teacher, the Rema, wrote: And in this time, when it is not the way of idolaters to do so, it is permitted ex post facto. Thus far his words. And consequently, also regarding one who slaughters to mountains, hills, and rivers in the previous siman, the law is also thus, for it is not the way to worship in this manner in this time [Shach and Taz]. And there is one who says that the laws of the previous siman apply even in this time, because it is a matter that was forbidden by a formal assembly, and therefore even though the reason has been nullified, it requires another assembly greater in wisdom and number to permit it, and it is impossible for us to permit it, for we are like ants compared to the ancients. This is not the case regarding the law of a pit, which the sages themselves permitted in a place where there is no suspicion, such as the cleaning of a house or a courtyard as has been explained, and now even in the marketplace there is no suspicion; therefore there is no concern in this [Kereiti U'Pleiiti]. And even this should not be permitted except ex post facto and not ab initio [as is clear from the wording of the Rema in the Shulchan Aruch, who changed from his wording in the Darkhei Moshe, see there; and it is known that that which was forbidden in the Shas has several facets to its prohibition, and delve into this].