Sometimes, logic needs to be applied to these type situations: Do you have the opportunity to drain EVERYTHING and then leave only one black valve open and see what toilet/faucet generates flow at that drain? Simple procedure. Can do this for each and every valve and see where the flow comes from in the trailer....???? Then just re-label the valves.
Do you have a grey tank valve? Does it work normal?
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired