I have a ’77 O’day 20 with the original through hull fittings – there are two, one for the sink/ice chest and 1 for the cockpit drain. I want to replace them, but am reluctant to fix something that isn’t broken (especially something that could sink the boat if not done properly!). I would appreciate any tips or suggestions relative to removing the existing fittings, what to install as replacements, how to install them, etc. Also, any suggestions as to what type of flexible tubing to use as replacements.Thanks.