一网打尽

一网打尽:

Literally means:

catch the whole lot in dragnet; round up the whole gang at one fell swoop

Actually means:

This phrase originally means catching everything in the water with just one cast of the net. It figuratively means catching or getting rid of all the villains or criminals.

本指把鱼虾兽类一网捕尽。比喻把坏人、罪犯等全部抓获或肃清。