Tony:
You try dawn dish soap and hot water?
Oh yeah I did. Many MANY times in succession. What hinders progress is the inability to get down in and SCRUB the interior. I finally decided that since the barrels would be utilized horizontally for storage, I could probably get by with cutting a "hatch" into their sides, which I did.
Then I could reach in and scrub, which did the trick. As far as odors, I have the best luck with simply leaving the container open to the air, and waiting. Flushing with air as you suggested seems to me like an excellent idea, and would probably hurry the process along.
By the way, if odor is a concern, avoid reusing food safe plastics that once contained pickles.....wow.
