FYI: I split this conversation out into its own thread and moved it to the Q&A forum.

I disassemble every keg before it gets filled. My cleanser of choice is TSP. It is strong and rinses away easily. I scrub everything, inside of dip tubes, included. Rinse like crazy and reassemble. Fill with Iodophor solution to sanitize and don't forget to get it in the dip tube (with pressure) and the CO₂-in tube (invert keg and depress valve to drain a bit into the tube). Let stand, then dump. Don't forget to empty the tubes. Purge with CO₂ and add beer. Seal, then purge again with CO₂. Pressurize and wait.