Bubbling toilet ....

Same type thing happened to my neighbor 3days ago. He started to back flush the black tank, then went across the street to help a neighbor. Water started running off the roof of the motor home when his wife called him home. They didn't flush the toilet though.
Hope everything is going good for you and Karen in Texas.
We're in Gulf Shores, AL.

Hockster

Hopefully, while flushing the black tank, these friends had the dump valve in the open position. I know what can happen if you leave the valve closed and forget about it with the flusher running. Trust me, it's not a pretty sight. I've since started using a clear adapter at the RV's sewer connection and stand there if I decide to close the dump valve. I wait about 5 minutes and open the valve again.

I have a clear adapter and also stand by the controls while flushing.
In the case of my neighbor, his valve was closed and the water came out the roof vent from the black tank.
I guess he has done this before.
You have to do one thing at a time, or clean up the mess later.
I can't even imagine the mess this causes.
I try to do this first thing in the morning before everyone else is up, I have less distractions that way.

Hockster

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When I'm dumping and/or flushing the black tank, I don't leave the UDC. I also tell the wife that the toilet is off limits until further notice (so I warn her ahead of time).

While flushing the black and gray tank we use a clear flush valve. We always stay outside at the controls. Nobody is inside till both tanks are empty and ready for the next use.