Found that someone had decided to store unused 2" Angle Cable Tray Support Assemblies under BSC1.  Sliding these in, the Feet on the Assembly was just the right height to hit the valve knob and turn it.  Fortunately, the drain exit is capped and no leak occurred.  Please mind the caution tape and be aware of the pushing and pulling things in and around the low dark places where HEPI resides.