I have a short hose connected to the flush.
I use the same hose I use for water if dumping at my site.. I let it run a few minutes after disconnecting to flush it.
I recommend getting a short clear extension so you can see what is coming out.
I think it works best to turn on the flusher and open the valve until the flow slows down. Then I shut the valve and let it fill up 4-5 minutes then open the valve again. Repeat several times until no more tp or stuff comes out. I drain the gray in between filling the black saving some for the final rinse.
I was surprised how much stuff comes out after it drains the first time.