I have a couple of kegs dedicated to dryhopping. I use a Surescreen on the diptube, purge the dryhop keg, hook CO2 up at 2PSI to the liquid out while opening the bail to dump in the dryhops. I let that run for a little bit.
Then I push beer into the dryhop keg from the fermenter. dryhop for however many days I want, cold crash under CO2 and then push the beer from the dryhopped keg into a fresh, purged serving keg.
works well for me.