Black tank flush questions

I did try the flusher since asking the question. It acts like it is clogged or maybe the backflow valve is stuck or installed backward. When turned on water goes nowhere. It's like there's a kink in the hose. Looking in the toilet with it running there is no spraying in the tank or sounds of spray. I'll check it when I get home or a slow day on trip. I hooked up the spray wand and it did the job.there is a door right at the toilet on this tt so very convenient for the wand anyway.