无底洞 (wúdǐdòng) a bottomless pit that can never be filled; insatiable desires
Usage:
“无底洞”本义指填不满的坑，因为看不到底部，形容满足不了的欲望或干不完的事情。
The literal meaning of “无底洞”is a bottomless pit that can never be filled since it’s failed to see the bottom. It is often compared to insatiable desires or the work can never be finished.
Sentences:
1、Nǐ búyào jiè qián gěi tā, dǔbó jiùshì yí ge wúdǐdòng.
你不要借钱给他，赌博就是一个无底洞。
你不要借钱给他，赌博就是一个无底洞。
You must not lend him money because gambling is a bottomless pit.
2、Zhè ge xiàngmù bù néng zài tóuzī le, jiǎnzhí jiùshì yí ge chīqián de wúdǐdòng.
这个项目不能再投资了，简直就是一个吃钱的无底洞。
这个项目不能再投资了，简直就是一个吃钱的无底洞。
We can not invest in the program as it is indeed a bottomless pit for money.
