What does this valve do?

[RAH]

What does the valve on the left do? This is a picture under the dinette of my 2013 FC 30. The valve on the right is the fresh water tank drain, when turned water gushes out of white plug under trailer until the FW tank is empty. When I turn the valve on the left, water drips (trickle would be overstating it) from a red plug under the trailer.

So what does the valve on the left do?

[Roadtoaster]

My guess, low point drain for the hot water lines. Should be one somewhere for the cold side.