How do I correct the slow/low water pressure in the device?

I had a problem that started with my Keurig K70 about a week ago. It was working just fine, made coffee as usual, and whenever the drip started slowing down, we would just clean the cup liner, and things would be back to normal. Now, even with the extra cleaning, the water pressure almost slows to a drip when making coffee. Without a K-Cup inside, the water runs okay, but it also sometimes starts slowing to a drip. What do I need to get to inside the machine to clean or replace so that it goes back to normal?