If they are plugged up, is it because you have galvanized piping?
If you do, then the best thing to do would be to replace the entire set up. You DONT want to "root out" galvanized piping, because all your going to do is get rust stirred up, and all kind of gunk.
(Believe me, I did this, when I first got this house I am living in, I rooted out all the pipes by shoving a rod through them, and then got to thinking, what am I doing? I am NOT going to DRINK out of this pipe after all the rust I have seen coming out of them! So, I went and put plastic lines in, until I got around to putting in 3/4 copper piping later on.