https://www.japanesefoodguide.com/masu-sake-in-a-box/
‘So on the point of spilling, just what is the “proper way” way to drink sake served to overflow? “There’s no specific etiquette,” Hioki told me. “This overflow pouring is hardly a refined practice, after all, and you’d never see it in a formal situation. But if I had to offer advice, I’d suggest drinking down the sake in the glass until there’s room to pour the overflow into the glass. Then set the box or saucer aside.” ‘
WearyTravelers.net 