"Drain the swamp" originally means to get rid of the malaria-carrying mosquitoes by draining the swamp. Figuratively, "drain the swamp" means "to exterminate something that is harmful" or anything that most of the people hate such as corruption or government waste. This term is especially attractive for politicians during campaign.

To empty the foul contents of one's rectum into public drinking water.

A phrase used by political hacks to rally voters to their cause by promising to remove their respective governments of corrupt sycophants and replace them with corrupt sycophants that donated to their own political campaign. Typically results in a swampier swamp.

To 'drain the swamp" is to remove water from a fetid low-lying area to make room for the effluence of your own cesspool.

Going number three; Going number 1 out your number 2; having diarrhea; Trump's presidency.

The act of performing cunnilingus on a woman during her period.

Taking out the middle man