Keurig or Tassimo sealed cups are popular when making coffee, because of their ease of use and uniformity of brew. But they also require more cleaning because its more complicated than a standard automatic drip coffeemaker.
You can thoroughly clean your single-cup coffeemaker using an old toothbrush and vinegar. Here in the video below, as demonstrated by housecare weblog Clean My Space, is a tutorial that shows you how to clean your standard Keurig coffeemaker, by hand.
Clean any white crusty buildup (mineral deposits) with a touch of white vinegar. When the dishwasher is finished, reassemble your Keurig.
After that, run vinegar through the machine to create a descaling brew to remove mineral deposits in the internal workings of the coffee maker. And fill your water reservoir halfway with white vinegar and run several brewing cycles with no K-cups to get rid of the vinegar and rinse it out of the reservoir. Do this a few times as you don't want leftover vinegar in your coffee.
This routine will take around 15-20 minutes but you don't have to do it very often.