Also even with a limited drain angle.....stuff flows down hill. So after dumping black tank fill it back up and dump again...repeat as necessary.
Having a clear adapter connected between end of dump line and sewer hose lets you 'see' how the stuff is flowing and when it's clean.
Then do a quickie flush of lines using the Flush King. As stated water flows under pressure just one way.....to the lesser pressured direction.
You are waiting until black tank is full/very full before dumping...right?
The 'stuff' in tank is carried out by the high volume/weight of the liquids. The higher the level before dumping the better the stuff gets evacuated.
Then after completely dumping/rinsing......add a few gallons of water back into tank so bottom of tank stays wet......less likely for stuff to stick to bottom, dry out, pile up and stink.
