This Halacha is an excerpt from our Sefer
Must one have separate sinks for meat and dairy dishes?
It is proper to have two separate sinks, one for meat and one for dairy, and so is the widespread custom of Jewry today. Doing so escapes the Halachic questions that can arise when using the same sink. It is proper that each sink contain its own faucet, its own drainage system, and be some distance from each other. Nevertheless, from the letter of the law, it is permitted to use the same sink for washing meat and milk dishes, if certain conditions are fulfilled.
Using the same sink for meat and milk dishes: If one only has a single sink available in his kitchen, then it is best to designate the sink for the most common use in one’s home, whether meat or dairy, and purchase a sink insert to use when washing the opposite dishes. One is to avoid pouring hot Yad Soledes water, or turning on Yad Soledes faucet water, while washing the dishes in the sink insert, if the water drains directly into the meat sink. After using the sink insert, one is to clean the sink from any dairy residue that may have escaped into it. If one does not own a sink insert, he may use the same sink for washing meat and dairy dishes if the following conditions are fulfilled:
- One cleans the sink from residue prior to placing the meat or dairy dishes into it. [It is difficult to determine whether a sink is cleaned of fat and oil residue through a taking a mere glance, and hence one is to wipe the sink with a sponge and then feel with his hands to verify that in truth no residue has remained.]
- One does not pour hot food [especially hot meat, or dairy] into the sink unless the sink is clear of any dishes.
- When washing the dishes, one is to use less than Yad Soledes water.
- One does not allow a vessel to remain in the sink for 24 hours.
Sponges: Initially, one is to designate separate sponges for washing meat, dairy and Pareve dishes, and so is customary of all Jewry today. See the section on “Sponges.”
Sink backup with same drainage system: If one’s meat and dairy sinks share the same drainage pipes, one is to look out for backups in the system which can cause meat and dairy residue to enter each other’s sinks. In the case of a backup, one is to make sure that all the vessels in the sink are removed within 24 hours and cleaned well with cold water. Likewise, the sink must be cleaned of the mixed residue within 24 hours.
What is the law if one found a milk dish in his meat sink or vice versa? See Chapter 8 Halacha 31!
Koshering a sink: The Koshering of a sink is dependent on its material. A metal sink can be Koshered through Iruiy Keli Rishon. Most sinks, however, are made of porcelain or enamel which are non-Kosherable materials.
Background on Pouring from a Keli Rishon
Poured from Keli Rishon onto meat/milk vessels:
Poured hot Keli Rishon water onto clean meat and milk vessels: If one poured hot Pareve Yad Soledes Keli Rishon water onto meat and milk vessels, then if both meat and dairy vessels were clean, everything remains permitted even if these vessels were Ben Yomo. [However, regarding a case that one poured onto an Issur and Heter pot, some Poskim rule that everything is forbidden if the Issur pot was Ben Yomo. However, according to the Rama, the Heter pot would remain permitted.]
Poured hot Keli Rishon water onto dirty meat and milk vessels: If one poured hot Pareve Yad Soledes Keli Rishon water onto meat and dairy vessels which contain meat and dairy residue, some Poskim rule that nonetheless, everything remains permitted. [This applies even if the water poured does not contain 60x versus the residue.] However, other Poskim rule that everything is forbidden. [Practically, one may be lenient in a case of great loss. This applies even according to the Michaber and Sephardic ruling. If only one of the vessels had food remnants while the other was clean [whether or not it was Ben Yomo], then the clean vessel becomes forbidden. Likewise, if the water poured contains 60x versus a Kelipas worth of the residue of one of the vessels, then only that vessel is forbidden.]
 See Hakashrus 1:13-19
 Minchas Yitzchak 2:100
The reason: This is due to several reasons: 1) As it is common to pour hot food into the sink, as well to use hot water to wash the dishes. Hence, if the sink would be used for both meat and dairy, the sink and possibly the dishes inside would become Treif. For example, if one pours hot water to wash the meat dishes and then poured hot water to wash the dairy dishes, some Poskim rule that the dairy dishes absorb from the Treif taste absorbed in the sink, and become forbidden. If the sink was not cleaned of meat residue, this is certainly a problem according to those Poskim. [See stringent Poskim in Chapter 8 Halacha 30D] 2) Another issue is regarding meat and dairy foods resting in the sink for 24 hours which would prohibit the sink due to the rule of Kavush, and likewise prohibit any vessels that soaked in it during that time. 3) All this is aside for the possibility of mistakes occurring, such as pouring a hot chicken soup into the sink while the dairy dishes are resting inside, thus prohibiting all the dishes.
 See in great length Igros Moshe Y.D. 2:42 for a defense of the custom to use the same sink for washing meat and then washing dairy dishes [separately] and a Halachic analysis on the power of pouring from a Keli Rishon. This response of Rav Moshe was to the prohibiting ruling of Rav Halbershtam who understood that based on the rule of Iruiy Keli Rishon, one may not wash dishes in the same sink; See Yabia Omer 5:33
 See Minchas Yitzchak 2:100; Igros Moshe Y.D. 2:42; Hakashrus ibid
 As if the hot Yad Soledes Iruiy Keli Rishon water touches the meat sink, it causes the sink to absorb the milk residue that is in the sink insert and prohibits the sink. This then cause issues with being allowed to use the meat sink for hot water washing. See Chapter 8 Halacha 30D! See however Igros Moshe ibid who is lenient in this matter.
 Technically, if hot water is not being used, there is no issue with having meat residue in the sink while washing the dairy dishes. However, since it is possible that residue will get stuck to the vessels and will go unnoticed in the cleaning, therefore one is to clean the sink beforehand. Likewise, if one leaves the vessels in the sink for 24 hours together with the meat residue, everything becomes forbidden unless the water contains 60x the residue.
 Since the sink is considered Treif due to its use for pouring hot meat and dairy into it, pouring even hot Pareve food onto the sink while dishes are there can cause the forbidden absorbed taste that is in the sink to become absorbed into the dishes. See Chapter 8 Halacha 30D!
 If one uses Yad Soledes water it can cause the forbidden absorbed taste that is in the sink to become absorbed into the dishes. See Chapter 8 Halacha 30D!
 This is due to the issue of Kavush Kimivushal, as since the sink is Treif due to the dual usages of hot pourings, therefore one may not initially soak food or vessels in it for 24 hours, even though Bedieved everything remains permitted as it is in any event not Ben Yomo by that time.
 See Hakashrus 1 footnote 26
 Rama 95:3; Shach 95:20
 The reason: According to the Rama, the reason is because the pouring of a Keli Rishon does not have the ability to cause the taste absorbed in the pots to come out. [Rama ibid] According to the Shach ibid, it is permitted because it is Nat Bar Nat and is a case of Iruiy Keli Rishon. [Shach ibid;]
 Shach 95:20; Kneses Hagedola 95:53; Minchas Yaakov 57:23; Peri Chadash 95:17; Kreisi 95:11; Lechem Hapanim 95:22; Chavas Daas 95:19; P”M 97 S.D. 20; Kaf Hachaim 95:47 and 52
 As according to the Rama, Iruiy Keli Rishon does not have the ability to remove taste from one pot and transfer it to another
 See Igros Moshe Y.D. 2:42 in great length for a Halachic analysis on the power of pouring from a Keli Rishon.
 Rama 95:3
 The reason: As the pouring of a Keli Rishon does not have the same ability as does a Keli Rishon to cause the pots to absorb from each other. [Rama ibid]
 Shach 95:20; Taz 95:12; Rashal Kol Habasar 64; Kneses Hagedola 95:53; Minchas Yaakov 57:23; Peri Chadash 95:17; Kreisi 95:11; Lechem Hapanim 95:22; Chavas Daas 95:19; P”M 97 S.D. 20; Kaf Hachaim 95:47 and 52
 The reason: As the pouring of a Keli Rishon has the ability to cook and transfer taste into a Kelipa’s worth of the pots, and hence the foods all become forbidden, which in turn prohibits a Kelipa’s worth of the pots. [Shach ibid]
 Shach ibid; Kneses Hagedola 95:53; Minchas Yaakov 57:23; Chavas Daas 95:19
Other opinions: Some Poskim are stringent to prohibit the vessels even in a case of great loss. [Peri Chadash 95:17; Kreisi 95:11; P”M 97 S.D. 20; Kaf Hachaim 95:52]
 Taz ibid; Lechem Hapanim ibid; Poskim ibid
 P”M 95 S.D. 20; Zivcheiy Tzedek 95:35; Kaf Hachaim 95:53; One must say in their intent that not everything is permitted as even if there is 60x versus the residue of one vessel, it nevertheless absorbs from the residue of the other vessel and becomes forbidden.