I have dry hopped 2 ways:
1.) whole hops, loose in secondary for 2 weeks
2.) in a bag, in the keg
The whole hops in the secondary worked great!! It was a Pseudo St Rogue Red clone. I say Pseudo because I changed 1 hop, I dropped Chinnook and used Columbus. I dry hopped with .5 oz of Crystal, .5 oz Centennial and .5 oz of Columbus.
In keg did not work so well, the first time I used .5 oz of Kent Goldings, whole, and it was ok, the second is(was) a failure. I made an APA that was really good and tried a new hop that I had just recieved, Palisade, and found it is not a good hop for dryhopping!!Turned a really good beer into an undrinkable brew!!Oh, I do not treat the hops before dryhopping, I just put them in, but when using a bag, I sanitize that!!