Confused on tank drains

[Triple GGG]

Thanks Chuck and John for your insight. Everything does look factory (but what do I know) as there doesn't appear to be any signs of cutting holes etc. It is supposed to be designed to camp down to 0. When I saw that I was wondering if that one section would not freeze. There was very little drained when I pulled the gray valve (by listening only) which makes me thinks this is a tank the kitchen sink drains too. Will continue to do trial and error.

John the "blue PEX" strung on the rail is actually the water hose. Since this camper is setup on the lake the previous owner zip tied it off the ground.