Help!! Black tank flush winterization issue

[mtnlvr]

So, I winterized my Solera recently but needed to use it for driving down to LA for Thanksgiving last week. I decided to use only the toilet and black tank. I carried gallons of water for flushing. I also put plastic tubs in the sinks using my water jugs only. They were then emptied outside or down the toilet.
Monday, after finishing dry camping at SP, I needed to leave my MH in the shop for some repairs. It will be there for several weeks. I drained the black tank. The lever was set on "winterize". I decided to try the black tank flush, thinking it went straight into the black tank and would then bypass the other plumbing lines. I then walked inslde with a couple gallon jugs that I was planning on dumping down the toilet to rinse further. I was shocked to find water on my floor inside!
So, I'm guessing the black tank flushing was a big mistake to try in winterize mode?? Help!!

[5picker]

Had you ever used your black tank flush before?

There are lots and lots of reports here and it is not uncommon for the inexpensive (cheap) plastic backflow/anti-siphon valve (usually located under the bathroom sink) to go bad or leak from the very beginning.

Replace it with a quality brass valve and you should be good to go.
Your winterizing valve should have nothing to do with this failure.

[mtnlvr]

Great thanks! I will change out that valve. The water did come inside under the bathroom sink plumbing.