If you use tap water like I do (and your city water stinks, like ours does) then over time the inside gets a little calcified and needs DE-Calcified. Have you ever done this before? It's super easy!
Take your coffeepot and mix half water and half vinegar. I used 3 cups vinegar and 3 cups water. Put that in your water reservoir.
Turn on. If yours grinds beans like mine, make sure to turn that feature OFF before you do this or bad things will happen to you. Bad things.
Let it brew away on the vinegar concoction and when its about half way done, turn it off. You want to have that vinegarry water all throughout the tubes and machine so its sitting in there cleaning everything out. Let it sit for half an hour then turn it back on to finish brewing.
After that throw the gross water away, fill the pot with fresh water and brew fresh water through it. Then do this again, just to make sure that the vinegar taste is out. After all who wants vinegar coffee? Bleh!
So there you have it. How to clean your coffeemaker. :)