During intimacy if a husband drinks his wife's milk, is it necessary for him to rinse his mouth immediately or it can be done after completing sex?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Milk of a woman is pure.  Therefore, it is not compulsory to wash the mouth from it whether it is drunk during sex or otherwise.

However, it is better not to drink the wife’s milk to avoid acting against those jurists who are of the opinion that if a male who has exceeded the age of infants drinks milk of a woman she becomes his foster mother just as she becomes a foster mother of any infant who drinks her milk.

Allah knows best.