At least it didn't happen to our rig. Earlier in the week, we noticed that the owners of another 5th wheel trailer on our street had emptied out the contents of their basement. We thought maybe they were cleaning house or reorganizing. The following day, everything was still out and we saw a fan that we know is used to dry out water damage. Oh oh.
When we talked to them, we learned that the woman in the motorhome next door had heard water running. She checked her own RV and couldn't find anything. Then she noticed water dripping off the roof the the 5th wheel--and it hasn't rained here. She then went to the woodshop and pool to find the owners.
What happened? While the water in the park was turned off to fix a leak somewhere, workers also came and replaced the water faucets for that site. They then reattached the hoses and turned the water on--for the wrong hose. One hose was the fresh water supply, the other went to the sewer system flush system. That is the one they turned on. So, when the water in the park was turned back on, it started flushing their black tank, which was closed. When it filled up, water came up through the toilet into their bedroom and shot up the black tank vent pipe, putting the water on their roof. That is what caused the dripping water.
Since the trailer was slanting just slightly toward the front, the only floor damage was to the bedroom. Some sewer water did get into the furnace ducts. What a mess! The park is taking care of all the damage, having new carpet and vinyl installed in the bedroom, etc.
The lesson? Only hook up the water to flush the black tankt when you want to do just that. Don't leave it hooked up. Needless to say, I'm not posting any pictures.