There is nothing worse, in my opinion (judge me as you will to my priorities in life) than tasting old, stale, rancid coffee flavors when drinking a cup of coffee.
Many coffee makers, particularly the thermal carafes, will stain due to the buildup of coffee oils and improper cleaning.
There is a simple tool you can use to combat this: oxygen cleaner.
For my daily routine I add a ¼ teaspoon of Joe Glo (available for $5 on Amazon) to the coffee maker brew basket after rinsing my carafe, brew, and let the cleaner sit in the carafe overnight. In the AM, simply dump and rinse before brewing. If you have a dirty coffee maker you may need to hit it a bit harder with a brush to remove all of the rancid oils present.
You'll definitely notice an improvement in taste... thank you for being a part of our coffee journey. Happy brewing!