Hi folks, so as posted above I did establish that the black rocker switch is for my water pump. The water inlet directly underneath the black switch remains a mystery. I followed the suggestion that it was for antifreeze (which would have been way more convenient than the inlet Iíve been using under the bed), but I attempted to winterize it today via that inlet and no luck.
Specifically, I closed the valve from the fresh water tank to the water pump, attached a hose to the water inlet in question and put the end into the antifreeze jug, switched on the water pump and called for water at the outdoor shower. The hose did not suck up water from the antifreeze jug...although a trickle (couple of tablespoons?) of clear water dribbled down the tube toward the antifreeze when I started the pump.
I continue to be stumped, as the thread for this water inlet is the same 1/2Ē size as the rest of the house plumbing. If it was to attach a hose to do a black tank rinse, as a Thor rep said when I emailed them, then it should be bigger - like the fresh water inlet. Right?
Open to suggestions....!