So if you use a dip tube in your BK, then when you run out your wort, once the level gets below the ball valve (or maybe before that, I guess) you are basically siphoning. I saw a DIY dip tube out of copper with an elbow designed for soldered connections but it didn't look like they were soldered. If they aren't soldered, wouldn't air get sucked in through the fittings and break the siphon?