A local (jewish/frum owned) store near me sells these little glass cups with mousse in them (produced by a non Jewish company). Do such cups require tevillah from the stores perspective? follow up question is, presuming it didn’t require (or it did but they didn’t toivel it, would I now need to toivel it
If this cup is made to through away after your done with it then it is disposable and no different from your wine bottle or pickle jar that you don't Tevilah.If you want to use it anyways then R' Moshe Finestine in Iggras Mosha Yorah Deah Vol 3 Teshvah 23 says that you dont need tivelah.
However, if the cup is meant to be take home and reused then there are two questions like you asked. The store does not need to toivel the cup since it made to sell and items that are not chaiev in tevila. (ill post sorces tomorrow)
You, the customer can use the cup now in the store will you eat since its a container for your food but, if you want to use it afterward you have to toivel it since you the end user have a chiev to toivel your kalim.
Rav Ashi says: With regard to those glass utensils, since when broken they can be fixed, i.e., remade, if one melts them down and fashions the material into new utensils, they are similar to metal utensils and also require immersion.
- Talmud; Avodah Zarah 75b
The Bais Yosef (Tur, Yoreh Deah 120) explains that when a Jew buys utensils from a Gentile, (even if the utensil is made to be used with food/a meal) for the purpose of resale, he does not need to immerse (toivel) the merchandise he intends to sell. This is similar to the case of a Jew who buys a Gentile's vessel (food vessel) for a non-food purpose. Since the buyer does not intend to use it for food purposes, it does not need immersion.
However, the second Jew who then buys it from the first Jew (who bought it from the Gentile to cut parchments or for food purposes but merely for resale and not personal use), for personal purposes of using the utensil for food during a meal, must now "toivel" it.
Furthermore, the storekeeper who is not obligated to immerse his utensils he bought from the Gentile for resale, cannot even do you a favor and "toivel" them all for you, since an immersion when not required is premature and is of no effect. (SEE: Shailos u' Teshuvos Minchas Yitzchak 8:70; based upon Rema, Yoreh Deah 120:9)
So what should a person do who buys such a glass cup of mousse and thereby becomes the new owner and wants to eat the mousse from it?
The Maharal Diskin explains that the laws of immersion of vessels do not require one to have to remove the initial food from a dish first, and then immerse it and then put the food back. (SEE: Maharil Diskin Kuntrus Achron 136)
A good example of this would be buying a bottle of beer or the OP's case of buying a glass cup full of mousse.
This is especially true for more reasons if the vessel in question is considered disposable. According to many authorities, disposables do not require immersion. (SEE: Chelkas Yaakov 2:47; Minchas Yitzchak 5:32; Rav Shlomo Zalman Auerbach Zt'zl in Shmiras SHabbos ”KeHilchasa: 9 footnote 41; Igros Moshe (Rabbi Moshe Feinstein Zt'zl) Yoreh Deah 2:40
I hope this helps your further study; If you have a real practical Halachic question; ask your Local Orthodox Rabbi. :)