Question: Is it permitted to tovel a metal kli inside a (narrow) glass kli?
Introduction: The Gemoro in Chagigoh (22a) quotes a Mishna in Mikva’os (6:2) that says that if one places some utensils inside other utensils and tovels them together, the tevila is valid. The Gemoro (ibid) differentiates between two different scenarios:
• In a situation where the outer utensil needs tevila (i.e because it too is tamei) then the tevila also works for the keilim placed inside, irrespective of the size of the opening of the outer kli (as will be discussed).
• In a situation where the outer kli does not require tevila then only if the aperture of the outer kli is the size of “shfoferes hanod” will tevila be effective for the inner keilim.
“Shfoferes hanod” is the width of two fingers and is the default minimum necessary to connect two bodies of water for various mikva’os ramifications.
The Gemoro (ibid) speaks out the reason for this differentiation: When the outer kli does not require tevila, standard mikva’os rules apply and there needs to exist a connection of shfoferes hanod to consider two bodies of water as halachically joined. Therefore, the water in the outer kli is only considered joined to the mikva when there exists the default minimum of shfoferes hanod. If the diameter of the opening of the outer kli is smaller than this amount then the water inside the outer kli is halachically detached from the water of the mikva and thus the inner keilim have not technically been immersed inside a mikva, and tevila for the inner keilim is ineffective.
However, when the outer kli being immersed itself requires tevila, since tevila is effective for the outer kli, the mechanism of “migu” allows tevila to be effective for the inner kli as well. Rashi (ibid d.h. migu) explains that tevila is effective even for a kli with an opening smaller than shfoferes hanod. We are forced therefore to say, that the water inside the kli (even though it is only connected to the mikva with less than shfoferes hanod) can be considered joined regarding the kli itself. And once this water inside the kli can be considered joined regarding the kli itself, it can also can be considered joined regarding the inner keilim.
The Shulchan Aruch (Siman 201 se’if 9) quotes this distinction (regarding keilim temei’im). The Remo (Siman 202 se’if 6) writes that when toiveling keilim inside other keilim, the opening of the outer kli needs to contain the size of shfoferes hanod. The Shach (s.k. 4) explains that this pertains specifically to a situation where the outer kli does not require tevila.
Therefore, in a situation where all keilim being toveled require tevila (e.g. because they are all keilim that were purchased from a non-Jew) one is allowed to tovel keilim inside other keilim, even if the outer kli does not have the size of shfoferes hanod in its opening.
Only in a situation where the outer kli does not require tevila and does not contain the size of shfoferes hanod in its opening it is not possible to tovel other keilim inside the outer kli, and if one were to do so the tevila in ineffective and needs to be repeated.
Discussion:
Let us now turn our attention to a situation where the outer kli is glass, and the inner kli is metal. Both glass and metal are obligated in tevilas keilim; glass midrabonon and metal min hatorah. As discussed before, when keilim are toiveled inside other keilim, if the aperture of the outer kli does not contain the size of shfoferes hanod, only if it itself requires tevila will we say “migu” that tevila works for the outer kli will the tevila also work for the inner kli.
Our situation (where the outer kli is glass and the inner kli metal) presents us with an interesting question: is it possible to say “migu” from a tevila d’rabonon to a tevila d’orayso? Or, since from a “d’orayso perspective” the tevila for a glass utensil is unnecessary, it is not possible to say “migu” to a metal utensil which is obligated in tevilas keilim min hatorah?
Several Acharonim take a stringent position and rule that since from a d’orayso perspective the outer kli is not in need of tevila, the aperture of the outer kli needs to be the size of a shfoferes hanod (Turei Even Chagigoh 21b; Lechem v’Simloh Siman 201; Gidulei Tahara Shu”t Siman 13).
Conclusion: One may only tovel a metal kli inside a glass kli if the opening of the glass kli is at least the size of shfoferes hanod.