I'll respectfully disagree about needing a sack. I go commando on my dry hopping, adding the pellets directly to the end of primary fermentation in the primary fermenter, then go to keg or bottling bucket.
If bottling, the first couple and last couple may have a couple floaties of hop bits, must most bottles will be very clear. It should all bits, hops or yeast, should drop to the bottom of the bottle if you lager the conditioned beer for a week.
And if you are bottle conditioning, do you always pour every last sediment filled drop into the glass?
Just Sayin'
BTW, it comes down to a personal process question. Maybe I'm just lazy. Maybe listen to Tasty's recent comments on Dry Hopping, I think He's moved away from sacks for dry hopping and gone the commando route as well (Jamil Show CYBI how to clone shows I think).
Cheers,
The Fool