Maybe a dumb question...I have a 2009 294 XLE. I'm winterizing my boat this weekend. There's a connection on the starboard side of the boat, behind the driver's seat on the edge of the hull. It just has a plastic cap on it. What is this inlet for? It has a filter screen and looks like a garden hose will fit on it. I am assuming that this is used to flush something, but what? Do I just need to have the drain plug out if I use it? If I do use it, do I then have to put air through it to prevent freezing over the winter?

Thanks!