Anti siphon valve

[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

[BB_TX]

My valve failed years ago before I was aware of the frequent failures of those valves. The outlet nipple broke completely off. I was sure I had winterized the flush system, but that made me feel as though I had overlooked it. But the area that it broke should have drained into the black tank even if I had not winterized.
I found the manufacturer name on the valve and ordered a new one. Upon receiving the new valve, I found the problem. The original and the replacement were both clear plastic. And the new one had multiple stress cracks in the valve. I marked those with a permanent marker and sent it back and received a refund shortly afterward. And then simply bypassed the section of pipe where the valve was and bought an external antisiphon valve. If I were going to replace that valve, I would definitely replace it with a metal one.
Look closely at the picture and you can see cracks in the body of the original valve.

Also easy to see how the valve works. Water pressure coming in the bottom pushes up the round white plunger with the O ring that seals and diverts water to the outlet port. And you can see that it has an atmospheric vent under the cap. That could well be the source of black tank odors some have reported.