47:17 Regarding containers that are made to hold wine for a longer time – that is, three days or longer – even if they belong to a Jew and a non-Jew stored wine in them only for a short time, they must be kashered using a process called eirui. This entails filling the container to overflowing with water, then leaving it sit for 24 hours. The water is poured out and the container is filled a second time. After another 24 hours, it is emptied and filled a third time. These three 24-hour periods need not be consecutive days; the water may be left for several days at a time, though this would still only count for one 24-hour period. Some authorities are of the opinion that if the non-kosher wine was in the container for more than 24 hours, then eirui is not sufficient to kasher the vessel because soaking something for more than a day is halachically tantamount to cooking. In such a case, hagalah – purging with boiling water – would be required. Whenever possible, it is advisable to follow the stringent position. 47:18 Because glass containers are smooth and hard, even if non-Jewish wine was kept in them for a long time, washing them thoroughly three times is sufficient.