The black knob opens the tank, is the red knob a regulator adjustment or just another valve in series? Looks like the small black knob is a bleed valve.
Yep you got it rightThe red knob is not a Knob but rather a protector for the gauge thats inside it mine does have a small gauge in the tank valve but is very small and hard to read
How do you fill this tank? Do you remove the gauge and hose assembly and fill through that threaded port. What is the threading on that?