I hear ya, the deadspace in my design would be the small ring of space around and up to the height of the locknut. I suppose it would take two paper towels to soak that much up though. It's probably equivalent to what's back-spilled from a traditional siphon tube.
Bobby -- I built my MLT and Electric HLT with bottom drains using the same weldless fitting approach you've described (minus the rigidly attached FB - mine is from Sabco and just floats without any issues, even when stirring). There is approximately 1/4 cup of liquid left in the bottom of each when I'm done. Getting the liquid out of the 8" horizontal pipe nipple is more of a bother for me than mopping up around the locknut.
I apparently lack the technical capacity to attach a picture, so I'll point you to Flickr: DrPaulsen's Photo Stream
For the most relevant images, check out the "Brewing Bench" and "Brewing Bench 3.1" sets. I think this picture, might be the only one to show the locknut: HLT with Bottom Drain