When racking beer into a 5 gallon keg from a bucket, I used to double purge a keg with C02 and fill the keg with the lid off and the racking tube dangling in the bottom of the keg. I’m usually then fighting with the hose to make sure it isn’t facing up splashing all over the place (hard to see in a keg that was just purged with C02). The last time I was watching my beer run into the keg, it occurred to me to just leave it closed and fill it through the diptube. I realize others have probably been doing this forever, but it was the first time I thought about it. I gave it a shot and it works pretty good (siphons a little slower I noticed). Although I’m sure there is still some oxygen getting in there as I understand purging is more of an oxygen C02 mixing step then a complete purge, but this at least seems like a slightly better method to minimize any oxygen during the transfer.
Remember to first release the C02 in the keg before you hook up the ball lock with the siphon hose attached, or you’ll have your racking cane go for a ride (mine did). Before you hook up the ball lock, it might be best to press the ball lock from the bottom and give the siphon a few pumps to get the flow going, which hopefully will push out any oxygen in the tubing. Once you get the beer flowing into the keg, keep releasing the keg vent to keep it going or just leave it in the open position. If you are going to be putting hops in the keg, this still works well. I just put the bag of hops in the keg prior to purging it with C02; I figure this probably helps remove any oxygen from the hops anyways.
For the setup in the picture, I purchased a threaded liquid ball lock and a swivel nut (barb), depending on what size barb you purchase determines the racking hose size. I’d probably just buy a barb to fit your current racking hose.
Examples of what I’m talking about:
Threaded liquid ball lock: http://www.midwestsupplies.com/ball-lock-liquid-disconnect-threaded.html
Barbed Swivel Nut: http://www.midwestsupplies.com/barbed-swivel-nut.html