Lift the handle to tilt the top back as you would to normally load the K-cup.
Remove the two screw underneath the cover and pop the tilting top off (two screws underneath release the top cover)
There is an in-line backflow valve just underneath this cover. You should see that it is clogged with residual coffee grounds. Remove it by removing the tie wraps and then pull off the hoses from both ends. Watch for the correct orientation when you remove it. You don't want to put back in backwards!
Run water back and forth through this valve and clean out the old coffee.
Re-install the valve (correct orientation) and to be completely sure of no leaks you may want to re-install some small tie-wraps on the hoses. I have not done this and mine hasn't leaked yet.
Enjoy coffee!