Using the Elliptical Marquee tool, hold alt and drag out a rough selection around the mouth of the cup
step 2 of 3
Clone the liquid out using a soft brush and using areas from the inside of the cups.
step 3 of 3
I didn't like the way the second cup cloned, so I made a selection around the first cup, copied it, and pasted onto the second cup. I then erased what didn't fit.