like a dose of salts
like a dose of saltsvery fast and efficiently. British informal
The salts referred to in this expression are laxatives.
1991 Peter Carey The Tax Inspector She's going to go through your old man like a dose of salts.
like a dose of ˈsalts(old-fashioned, British English, informal) very fast and easily: We’ll go through this house like a dose of salts, cleaning it from top to bottom.
Salts in this phrase are laxatives (= medicine that makes you go to the toilet).