Suburban IW60 Nautilus Tankless Water Heater?

Hi and thank ya kindly for replying to my questions about the Suburban IW60. I'm glad to receive any information from RVers who have this unit. I will get an extra flow sensor to have on hand. How exactly does the sink miser hook up to system and do you have to have it return in fresh water tank or can you loop it to come back around? Thank ya again kindly ??