[kgs]

AHA's kegging guide states: "Now it’s time to rack beer into the keg. To do this without introducing oxygen, first pull the pressure relief valve on the keg to drop the internal pressure to atmospheric."

https://www.homebrewersassociation.org/how-to-brew/an-introduction-to-kegging-homebrew/

Does that mean pull the PRV until the hissing stops? Up to now I have kegged by draining from the fermenter into the keg using a piece of tubing (my fermenters are all modified 5-gallon food grade buckets with spigots) then purging the headspace, and the beer is definitely better than when I bottled. But in the interest of reducing oxygen exposure I'm trying to work up the nerve to try this method.

[JT]

I think if you follow these instruction you will be disappointed when the keg you thought was empty starts bubbling into your fermenter. 
Dont pull the PRV.  If you are using the bucket spigot, hook the hose up to your black QD first (assuming ball lock leg since you mentioned PRV.  Also hook up a length of hose to the grey QD.  This will go into a jar of sanitizer or water. 
Snap the liquid disconnect to the post first and aim the open end away from your face.  It will blow sanitizer that settled.  As it winds down hook up the gas disconnect and put the open end in the sanitizer.  Now hook up to your spigot and drain.  I fill mine until beer comes out the gas post (I'm also using shortened gas tubes).  Then push a cup or so of beer out after filling. 

[kramerog]

I release most of the CO2 through the PRV.  I vent the rest through the gas out (via gas disconnect and hose) to purge the hose of O2 before connecting the gas out to my carboy to maintain a CO2 blanket over the beer in the carboy.

[hmbrewing]

I think if you follow these instruction you will be disappointed when the keg you thought was empty starts bubbling into your fermenter. 
Dont pull the PRV.  If you are using the bucket spigot, hook the hose up to your black QD first (assuming ball lock leg since you mentioned PRV.  Also hook up a length of hose to the grey QD.  This will go into a jar of sanitizer or water. 
Snap the liquid disconnect to the post first and aim the open end away from your face.  It will blow sanitizer that settled.  As it winds down hook up the gas disconnect and put the open end in the sanitizer.  Now hook up to your spigot and drain.  I fill mine until beer comes out the gas post (I'm also using shortened gas tubes).  Then push a cup or so of beer out after filling.

I brew 2.5g batches and ferment in 5g kegs. When time to package, I purge my receiving/serving keg with CO2. Then, I attach my CO2 to the gas in post on my fermenter. I then attach a jumper from my Beer Out on my fermenter to my beer out on my receiving keg. Ball lock disconnects on both ends, of course. I apply a small amount of CO2 pressure to my fermenter and very slowly unscrew my PRV on my receiving keg until I start to hear a hissing sound. At that point I stop and leave the PRV in that position for the entire fill. The hissing (which is essentially CO2 leaving my serving keg) continues throughout the entire filling process. Once done, I tighten the PRV and I'm done.

However, JT mentions a way of releasing the receiving kegs pressure without fiddling with the PRV and I love it! I never thought of simply attaching to the CO2 post on the receiving keg and just letting it bubble into a jar if sanitizer. That seems way easier than messing with the PRV. So I shall give that a try when I package my cream ale this week. Love it!

[ynotbrusum]

I have gas posts on most of my fermenter lids now and do a closed loop transfer to push by CO2 from the keg to fermenter to displace the finished beer going from the fermenter into the keg.  I purge both the liquid line and gas line first with the CO2 in the keg (stopping before the hissing subsides) then fully connect it up to the gas posts then the liquid side.  Then it gravity feeds with a little pressure assist.  Is it totally without O2 ingress?  Probably not, but it certainly is better than auto-siphoning, like I used to do....

[goose]

I think if you follow these instruction you will be disappointed when the keg you thought was empty starts bubbling into your fermenter. 
Dont pull the PRV.  If you are using the bucket spigot, hook the hose up to your black QD first (assuming ball lock leg since you mentioned PRV.  Also hook up a length of hose to the grey QD.  This will go into a jar of sanitizer or water. 
Snap the liquid disconnect to the post first and aim the open end away from your face.  It will blow sanitizer that settled.  As it winds down hook up the gas disconnect and put the open end in the sanitizer.  Now hook up to your spigot and drain.  I fill mine until beer comes out the gas post (I'm also using shortened gas tubes).  Then push a cup or so of beer out after filling.

I brew 2.5g batches and ferment in 5g kegs. When time to package, I purge my receiving/serving keg with CO2. Then, I attach my CO2 to the gas in post on my fermenter. I then attach a jumper from my Beer Out on my fermenter to my beer out on my receiving keg. Ball lock disconnects on both ends, of course. I apply a small amount of CO2 pressure to my fermenter and very slowly unscrew my PRV on my receiving keg until I start to hear a hissing sound. At that point I stop and leave the PRV in that position for the entire fill. The hissing (which is essentially CO2 leaving my serving keg) continues throughout the entire filling process. Once done, I tighten the PRV and I'm done.

However, JT mentions a way of releasing the receiving kegs pressure without fiddling with the PRV and I love it! I never thought of simply attaching to the CO2 post on the receiving keg and just letting it bubble into a jar if sanitizer. That seems way easier than messing with the PRV. So I shall give that a try when I package my cream ale this week. Love it!

I do the same thing that JT does when filling kegs.  It works great!.  One of these days I am going to dry hop in my conical fermenter rather than transferring to glass carboys for dry hopping (I currently do this so that I can have the conical ready for the next batch).  Although I do purge the carboys with CO2 by running the line in there and turning on the gas before filling, obviously, there is some O2 left in the carboy due to Boyle's Law of Partial Pressures and the fact that the pellets also have some oxygen in them as well.  But it is better than not purging them at all.  I then fill the kegs by pushing the beer out of the carboys and into the keg using the method JT describes being very careful not to exceed 2.5 lbs of CO2 pressure in the carboy for safety reasons.  All of my malty beers are kegged directly from the SS Brewtech conical after burping out the yeast.