Sorry to rain on the parade but a Flush King is designed to seal a pipe and build pressure against a blockage in that pipe. The assumption is that the pipe is COMPLETELY blocked thus allowing the King to build the static pressure in the pipe equal to the city pressure. If there is any passage of water through the pipe before using the King it will never build pressure and only flow water back into the tank. The likelihood that this flow of water will dislodge anything is the same as having filled the tank as normal and then draining.
To use water pressure in the absence of a complete blockage you need to be able direct the waters kinetic pressure directly at the blockage.
Take some 1/2 in copper pipe and adapt it to a hose. Solder an elbow on the end and solder just enough 1/2 in pipe into the elbow that you can get the pipe down through the toilet. Smash the end of that short piece of pipe, at a slight angle to the bottom of the tank, to create a fan spray. Now insert the wand and start spraying.
This is the same principle as the commercially available wands but with a higher volume of water being used.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles