I do rinse the lines out by hand with hot water before assembly. BUt don't sanitize.
Or contaminants that get in post-manufacturing I suppose. Unless it came in a sealed bag there could be dust, liquids, etc.
Contamination is not a huge deal post fermentation once the beer is packaged - not saying it is unheard of but it's not as easy as we make out soemtimes. And, while we are justified in being concerned about contamination, there is no need to be overly paranoid. Not all microbes are beer spoilers, in fact the vast majority are not. Even so, beer line is sanitary enough for packaged beer. There is absolutely nothing to worry about.