Squires original criteria was to avoid filling the muffler with fuel, only to have it go to waste...hence MinnFlyers one way fuel check valve, and overflow dot in the muffler pressure line. Filling would still have to be via a fuel dot in the third line. Filling from the top/muffler pressure line would cause fuel to be immediately gushing out of that third line.
One other item being overlooked is....if it is a gasser, (walbro carb) it will not allow fuel to flow to or through the carb under the pressure from filling the tank...however, a glow fuel carb has no such restrictions, and of course while filling the tank, you would be filling the crankcase of the motor as well. Not a good idea!
Thats where a little hemostat would come in handy to pinch of the carb line while refueling....assuming you can get to it.