Musty taste in beer lines

[Bobcatbrewing42]

I have a "Tru" kegerator with 3 corny kegs. The tower has two taps and I have line with a perlick on the third. The beer lines are all inside and kept chilled. Every time that I pour a beer after more than two hours have passed the first couple of ounces taste stale and musty and need to be dumped. If you pour off a little then it is fine but if you just fill the glass, the whole glass has a bit of off-flavor. Of course it is more noticeable in a light pale, than an IPA or porter.
Does anyone have a good method to completely clean out the lines and taps without dis-assembly? Does PBW work or use something stronger?

 

[grainbill]

back flush the lines, BeerLineCleaner works well, PBW if you have a way to recirculate through the lines..

 

[zachattack]

If the problem persists you can try a barrier tubing like Accuflex.