The fastest way to flush your colon is to use some colon cleanse supplements that you can buy online or over the counter.
Also a more natural way of flushing your colon is to drink some water and increase your fiber intake or drink some prune juice, apple juice etc.
Any foods or drinks that can get you pooping soon can help flush out your colon.
The best way to clean your colon overnight naturally is to use some Sea salt or Himalayan salt and mix it with water.
Take some Sea salt or Himalayan salt and mix the Sea salt or Himalayan salt with a glass of water and then drink it slowly.
Within a few hours you'll be needing to go poop and that will help flush out your colon.
The more you poop the more clean your colon will become.
Also taking Metamucil can help you go poop and when you do take some Metamucil or Sea salt or Himalayan salt in water make sure you're near a toilet.
You'll need to poop within an hour or so after consuming it and especially if you consume the Sea salt or Himalayan salt.
Taking some Castor Oil can also help get your colon clean by making you poop.
Another option to clean your colon is to take some Colon Cleanse that you can get over the counter.
The Colon Cleanse when taken often enough can keep your colon clean and may prevent colon cancer as well.