[mtlakejim]

If you have removed the check valve at the hose connection the line will likely drain back from bathroom vanity. And line from vanity to Black tank should drain to the tank all thanks to gravity. Chances of any black water draining all the way back to convieince center hose connection seem very remote to me. Even if it does, worst you get is a little nasty water in your plastic box and the ground. Not like it is going to contaminate your drinking water

Even though the line most likely self drains I still run pink winterizing fluid thru it. It’s not difficult to do the way I have things setup