There seems to be a lot of "anticipated efficiency" with black tank flush systems. Many people expect a device inside their black tank that "mimics a high pressure washer wand" while others expect a "strong stream of water that's directed at all the walls inside the black tank, effectively "washing" the walls to prevent buildup....
NOTHING COULD BE FURTHER FROM THE TRUTH !!!!!
When you consider that a holding tank is typically 4" deep on one end and 7" deep on the other, 24-28" wide and 60" long, with a "flush nozzle" mounted near the center of the tank, what really happens inside your black tank is a "couple of streams of water sort of aimed at various angles, add water to the tank, hopefully rinsing some of the debris off the tank walls.
Take a look at the three brands of black tank nozzles, look at the amount of water, the velocity of that water stream when connected to a water hose under "house faucet pressure and volume"... Then imagine that nozzle INSIDE a shallow, long box.... That's what's happening inside your black tank.
Of the three brands typically used, only one has a "rotating nozzle inside the black tank... Take note of how the narrator gets that nozzle to start spinning.... Are you (can you) reach inside your black tank to get the nozzle to turn ?????
There's a lot of "hype" about black tank flush systems... Most of it is just that, "hype"... Sure they add water to a black tank so you don't need to repeatedly flush the toilet to fill the tank during a "rinse" but realistically, the amount of water volume and the "paultry pressure" that comes out of the nozzle won't "clean your black tank"... It likely won't even reach the sensor "nails" stuck in the end of the tank, 30" away, and if it does happen to splash on one or two of those nails, there likely won't be enough force to break up a "gob of toilet paper and poo"....
Take a look at what's "really inside your tank" and don't expect more than it can deliver: