There is no real Hechser on 7-11 Slurpees. How do people drink them? Is going on the Star-K's list okay? What about soda from the machine? I found that 7-11 switches the spouts sometimes. So even if the soda is Kosher, what about other sodas that may have gone through those tubes?
Rabbi Sholem Fishbane has a comprehensive article about Slurpees here: http://www.crcweb.org/kosher_articles/slurpees.php
Regarding the nozzles of the machines, an article by Rabbi Dovid Cohen (http://www.crcweb.org/kosher_articles/fountain_soda.php) describes how the CRC came to the conclusion that it does not pose a kashrus concern.
The Star-K in this shiur discusses everything at length including what their list is all about, as well as all the issues:
However, it appears you need to sign up to access the above link. A quick workaround: the shiur is also available on iTunes Podcasts over here [it's the one dated 6/3/10].
And for reference: the list of the Kosher slurpees at Star-K.