slow drip from insulation around low point drains

The third valve is for the feed side of the water pump, it either allows flow from the fresh water tank below the flooring or it allows feed from the short hose "that goes nowhere".  You can use the short hose to feed RV Antifreeze (the pink stuff) into the water system for winterizing the water system.  The valve only controls the feed source for the water pump.  Hope this makes sense to you.  Have fun.

Maybe add half a gallon or so anti freeze into fwt, then run the pump to suck it into the line, should be good. You gotta sanitize the fwt in the spring anyway. 

StephenH "(If you empty the tank and run the pump until it is just pulling air, there will not be enough water in the line to freeze. )" Will this burn up the pump, running it dry with no water to source?

I was just outside (in the rain) and i think (i hope) i caught the source of the leak above the low point drains. The ac outlet outside needs to be caulked- water was dripping down the wall inside and maybe finding it's way to the low point drains insulation and dripping to the ground.

If you empty the tank and run the pump until it is just pulling air, there will not be enough water in the line to freeze. Then use the winterizing valve and hose to pump RV antifreeze through the lines. That will get the water that just air seems to miss. Be sure to bypass the water heater first. Drain the water heater by removing the anode rod after relieving the pressure. I use the air/RV antifreeze combo. This makes absolutely sure my pump and the various valves are protected from damage. Getting rid of the RV antifreeze residual taste in the spring is not that difficult. After sanitizing with bleach, follow it up with baking soda dissolved in water. That will go a long way to get rid of the odor and taste.