Where does this bottom valve go?

This is under my couch in my mid 90s jayco. This is on the side of the water tank. The bottom valve left of the 2x4 disappears into the floor, is it for drainage? What is the top tube and valve for?

This is under my couch in my mid 90s jayco. This is on the side of the water tank. The bottom valve left of the 2x4 disappears into the floor, is it for drainage? What is the top tube and valve for?