Avodah Zarah 33 - Idol-worship Pilgrimages
If a non-Jewish idol-worshipper goes on a pilgrimage, it is forbidden to trade with him when he is on the way there, but permitted when he is on his way back. On the other hand, if a Jewish idol-worshipper is going on a pilgrimage, it is permitted to trade with him on the way there, but forbidden when he is coming back. Why is this difference?
A non-Jewish idol-worshipper will certainly reach his destination and praise his deity for any successful trade. However, when he is coming back, his attitude is that what was - was, and he is not going back to give thanks to his idol again. In contrast, we assume that a Jew going to worship idols will change his mind. However, once there, and idol-worship being a new and fresh experience for him, he gets attached to the idol more than a non-Jew, and certainly will go back to praise the idol for any good deal he finds.
If wine of an idol-worshipper was stored in a leather or earthenware vessel, the proper cleansing procedure is to fill it with water three times, leaving the water in the vessel for at least twenty-four hours.
Art: John Singer Sargent - Bedouin Women Carrying Water Jars