Being new to a boat with a fresh water tank for the sink, I am wondering if/how this needs to be treated. Does anyone have this option and can advise as to how you maintain this? I read up on people explaining how to sanitize at the beginning of the season. I am more interested in knowing if there is some additive that needs to be added with each fill? I know we should not be drinking it but still don't want this water getting nasty in there. I also assume some type of RV antifreeze during the winter as I saw there was a lot of purple fluid in the tank when I bought it.