It is hard for us to know what flush system your rig will have - Ask the manufacturer.
Our last two rigs have had black tank flush system - multiple jets - and both did an excellent job.
Generally, I dump the black water tank, when the indicator show 2/3 full. If I have to dump before that, I add water using the flush system.
After turning on the water to the flush system and opening the dump valve, from inside the RV, I shine a flash light down the toilet. It has always looked clean. Next I run the flush system until the water exiting is clear. That has always been the case when I got back outside to the water bay. That's when I shut the water off, let it drain, close the valve, and dump the gray water tank.
Tom