Non-obvious solutions

1. Have the filter basket empty. If you use a reusable filter, remove it.
2. Fill the reservoir up to the top with two parts water (tap works fine for me) to one part white vinegar.
3. Brew it.
4. Dump it out.
5. Fill the reservoir, again up to the top, with straight water.
6. Brew it.
7. Dump it out.

If you’ve never done this before, you will not believe how well it works. The difference is most visible in a glass carafe, and is stunning.