I just chuck them in, unless I'm using a hops bag. If I use a bag, I sanitize the bag then put the hops in that. The problem with the bag- it's hard to get in a carboy and even harder to get out. But if I'm using alot of hops, I'd rather use a couple of bags. One time I dryhopped with an ounce and a half of leaf hops and lost quite a bit of beer to the hops when I racked. Right now, I'm dryhopping the 777 with two ounces of leaf hops and I have those in bags.
If I was using pellet hops, I'd just toss them in.