2,412. A Double Seal

Maachalos Assuros 13:7

Let’s say that a courtyard is divided by partitions with a non-Jew on one side and a Jew on the other, and there are two roofs – the Jew's roof above the non-Jew’s or next to one another but with partitions between them. Even though the non-Jew can reach the Jew’s side, there’s no concern that he might pour the Jew’s wine as a libation or impurify things that are ritually clean.

Maachalos Assuros 13:8

A Jew is allowed to entrust his wine to a non-Jew in a sealed container so long as it has two identifiable signs; this is called “a seal within a seal.” For example, if the Jew closed a barrel with a lid that doesn’t fit tightly – which is common practice – and then sealed the lid with clay, that’s one seal. If the container is closed tightly and he put clay on it from above, that’s a seal within a seal. Similarly, if one tied the mouth of a wineskin closed, that’s one seal; if he turned the wineskin spout inward and then tied it closed, that’s a seal within a seal. Any variation from the way people normally close something is considered one seal and putting clay on it or tying it would be considered a second seal.