I am removing with difficulty a submersible pump that is 21 years old and has failed. It is in a 300' deep well with 6" casing. The drop pipe is 21 year old (or more) galvanized 1-1/4" 20'joints. I have yet to pull it all. I am a diy farmer type. I don't know how much drop pipe there is. If I ever get it out I'm considering replacing with poly. Is this a good idea. Is there any advantage to using galvanized. Any disadvantage to poly?