I've since learned better, but when I first got my kegging setup, I put root beer on one of the lines. After that keg was empty, I decided to put soda water in instead. Unfortunately, the root beer scent is fairly strong.
Like I said, I've since learned that this is a problem and you shouldn't put root beer in there. But, here I am, having made that mistake. Is there anything I can do, short of replacing everything that touched root beer?
Clarification: Here's what I've all tried. I ran an entire keg full of oxyclean through the line followed by an entire keg full of baking soda water. On both, I ran the liquid through fairly slowly, letting it sit in the lines for a while before running some more through.
At this point, straight soda water still tastes distinctly of root beer, though when that water is flavored with orange, it masks it enough that I can't taste the root beer.
At the end of this keg of water, if I still taste it, I guess I'm going to replace all of the tubing up to the tower (which I can't figure out how to tear apart, actually), rebuild the keg with new O-rings and, if no one has any better ideas, I might just replace the entire tower too (thus having replaced everything that touched the root beer).
The take away for those who want root beer on tap, the best bet is to have the flavor syrup in a bottle with a pump (like the ones at the coffee shop) and just put soda water in the keg. That way, you can make your own soda flavors by mix and match and none of your equipment gets that root beer flavor in it.