تعريف ومعنى "[drain] the swamp"

What is the origin of the idiom "drain the swamp" and when to use it?

The idiom "drain the swamp" has a historical origin that predates its political usage. It can be traced back to the late 19th and early 20th centuries in the United States. It is often used in politics when politicians promise to get rid of bad practices and bring positive changes.