Okay all,
Flushed black tank after a few days of visitors. About a cup of black water came down around my pipe (right above sewer hose connection) and went on ground. Nothing else. Yes I had noticed my toilet bubbling right before I dumped. I had started flush a few seconds before opening valve Is this an overflow issue or are there more serious issues. 2019 - 3850 Bighorn.
Sounds like there's a blockage at the valve for the black tank. Given that the toilet is bubbling, the tank is probably quite full. You can try back flushing to move the blockage, but be careful about adding more water to the tank.
A clear twist-on backflush adapter and a twist-on gate valve will let you force water back into the black tank. You'll need to keep the grays closed while doing this. And again, be careful about how much water is added.
Don't use the trailer's black tank flush at this point. You could have very undesirable results if the black tank can't accommodate any more water.
Here's a clear adapter with built-in gate valve. Your local RV dealer may have this as well. For regular use, another
twist-on gate valve is a good addition to the sewer outlet. This one would stay on the sewer outlet while traveling. Open the valve after attaching the clear adapter and sewer hose. It'll keep from spilling black water when you uncap the outlet. Also, if you have a slow leak at the black tank valve, it'll keep you from losing all the water in the black tank, leading to a poo pile. Keep the handle at 1 o'clock so the weight keeps it twisted on.