밑 빠진 독에 물 붓기 (pouring water into a bottomless pot)

밑 [n] The lower part of something, a part that forms the bottom or lower part of something.

빠지다 [v] fall out, For the bottom of a vessel, the sole of a shoe, etc., to fall off

독 [n] jar, a tall, bulging earthenware jar in which jang, fermented paste, alcoholic beverage, kimchi, etc., are stored.

붓다 [v] pour, to put liquid or powder into something.

>> This expression is an idiom used to describe a state in which no matter how much effort or money is spent, there is no limit and no reward. The expression is used to describe a futile effort, or when one’s effort goes to waste. 

>> The expression is often used for situations related to money, as in describing the shortage of money someone may feel despite working hard because there are so many things to spend money on, or as in the dialogue, when someone spends money endlessly helping others.