I have been fermenting in a 5 gallon pin lock keg the last few batches. I brew 3 gallon batches, so, the size is perfect. I use a spunding valve to naturally carbonate the beer and then transfer under pressure to a sani-purged keg.
I tried using a cut dip tube. That worked okay, but, I also have tried using a Clear Beer Draft System (
http://www.clearbeerdraughtsystem.com/) in the fermenter. The clear beer draught system works well for this application.
Here a couple of pics stolen from Clear Beer's website.
The float keeps the beer inlet above any trub. The float is in the fermenter from day one. I was worried it might get clogged by krausen, but, so far that hasn't been a problem.
The float is stainless steel.