[JRTJH]

The water hose connector at the sidewall of your trailer has an one way valve inside it. The O-ring in that valve sometimes sticks or swells and makes it hard to open. If that happens, water won't flow into the black tank flush system. Sometimes waste (mainly toilet paper) will hang up on the flush system nozzle. If it dries there, it will act like "concrete" to stop the flow of water through the nozzle. Those are the two most probable causes "outside the anti-siphon valve which is located under the sink.

The first thing to check is the anti-siphon valve. You can check it by using a compressor at low pressure, cupping the valve in your hand and blowing air through it. Air should flow in one direction and not the other. If it "rattles" and air flows, then it's good unless it's dripping into the cupboard where it's located.


Sometimes the PEX hose will crimp either in the sidewall of the trailer or at the entry to the black tank and stoop water flow, but since your system was working last season, the hoses should not have "shifted to crimp" so that probably is not the issue.

If I were you, I'd fill the black tank from the toilet, add some black tank cleaner/digester, let it sit for a few days to a week, then dump the tank and try the black tank flush system. If it's that "concrete plug" over the nozzle, the water soak with digester should soften it enough to allow it to be washed off the holes in the nozzle. If that doesn't work, then the second place to look would be the water inlet on the side of your trailer.

Let us know what you find and good luck.