Just rub it off with a rag. Ya have to scrape it a little with your fingernail to get it started.
And if really a mess or prroblem - I use a little acetome on the rag!!! (on the black or sliver metal sinks).
And I definitely agree with what your doin. The tape doesn't work nearly as good as good ole heat sink compound. I keep a thermal diode sensor on the heat sink so I can compare the internal CPU sensor and the heat sink. Sotra cool cause ya can watch the sink absorb the heat!!!
Using cheap Radio Shack heat sink compound($3.99 - silicone zink oxide) really does pretty good. I only get 3 or 4 degrees C difference in CPU and sink, and it stables 2C around 15 minutes of steady use. . Much better than tape that gives a 5 to 8 degree C diff. But tape is better that nothin which gives ya a 10-15C diff...
Really cool stuff - cause I was just recently very impressed with the preformance of heat sink compound fixing an over heating problem child I had.
And I'm also mildly impressed with these cheap little disk cooling fans ya put in 5.25 bays. Had a tight little mid tower with the temp over 120 in the top of the box( even with a case fan in the bottom). Put that little plastic disk cooler($18) in an empty 5' bay(also turned the fans to blow out insead of in) and took over 12-15 degree F out of the box and 7-8 C off sink and CPU...
(Box < 105F, Sink & CPU 45-50C, never > 4 diff, workin!)
That problem child ain't a problem child no more!!!
Will try some Artic Silver and check its Delta.