Ok guys.. new to boats. Got my 1st boat. I have a 2012 Tracker Pro 165. It has 3 inlet/outlets in middle of transom near bottom. I know one is main drain, one is inlet for the livewell but not sure what other black one is? Is it drain for livewell? What stops it from backfeeding into livewell? Just the drain tube in place? The bilge drain is higher up above water line of course. Thanks for any help.