There’s a very simple solution to this problem, but you may not like it. Tell everyone the coffee pot needs to be washed every day and put up a sheet assigning the task to people. When that person washes the pot, they sign the sheet. If you have a camera in the break room, it’s even more effective.

Then you can see on the sheet who was supposed to wash the pot but didn’t (or did it poorly). It will not work with people who say it’s “not their job”, but at least the problem is clearly visible.