Ours has the flusher, with an attachment, to put chlorine tablets in and sanitize the tank as it flushes.
It has a ball valve that leaks. It is plastic. The back flow preventer is nearer the tank. Water still dribbles out from the little plastic quick connect, when you disconnect the flushing attachment or hose. Aggravating but clean water.
Watch the tanks levels as you fill them to flush. A moment's inattention and you will be swelling tanks and bit more you may have water up into the shower or the toilet flange give up.
Our gaauges are in the coach os it is connect the hose go into the coah and watch the level as the black tank fills go out swith to gray tank go in the coah and wait until it shows full.
Go out open the blaacck tank and turn the handle to have clean water enter the tank and stir things around. As the tank empties you will hear it burp.Let it run for fie minutes, the manual says more. Close th valve and put a few gallons like two to five into the black tank.
Turn the fill valve to gray water tank and open that valve. It will take a little longer as it is larger.
After it drains let it fulsh a minute or two close drain valve and let a couple gallons in.
Cut off water, cut the little ball valve off, remove the hose, after turning off spigot, slowly, and unplug the flush gadget.
We use the Rhino hose which takes the considerable pressure of a full tank draining better and it has a opaque elbow end where it connects to the sewer, so you can see when clean water is finally going through.
I have had a couple of the thin sewer hoses burst. Not pleasant and birds etc peck holes or chew holes in them, or step on them with gravel under then and develop leaks and geysers when flushing.
Had one of the red shot extensions, similar to the Rhino material burst in one of the pleats last trip.