The plug on the left is used as a blow out valve entry point, or to introduce antifreeze to the water system. The pull tab on the right is the low point drain for the freshwater tank and the rest of the system. Mine is slightly different as I have 2 drain valves one on each side of the pump.
The fresh water fill tube has a slightly uphill run depending on how your parked, I usually need full pressure of the hose to overcome that to fill the freshwater, once it starts flowing it does fine till its full. I never thought about adding bleach to the hose that is a good idea i'll try next time.
2013 Thor ACE 29.2