I thought I'd throw this out to anybody about to start heating up some steel.  ALWAYS make sure your tubes are clean.  To do this after you have mocked up the frame and are ready to start brazing, sand the miters to get all the burrs out....next degrease the tubes with something like "simple green" (which is what we use) some folks actaully wash their tubes in a sink with "Joy" dishwashing soap and then dry it off with acetone.......the point is, when the tubes are as clean (degeased) as you can possibly get them the flux will work like magic and you will end up with smooth fillets.  Braze on!

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Smokebikes..........mountain fixies

Yep..what he said. The cleaner the better. Our wash system is a 4 part wash & rinse.
We used 2" pvc tubes and capped them with one end glued and one end screwed.They are all sitting in a nice little rack Gabe built.
The process is this..
1- degreaser( simple green)
2-water rinse
3-Alcohol rinse
4- final alcohol rinse....
about 30 seconds in each is sufficient
Oil from your fingers,cutting fluids,bug-a-boos inside the tubes will jump out and
bite you during brazing...yep we found that out the hard way..