What is this? ( a plumbing question )

We replaced both of ours (one on each black tank flusher) with Watts LF288A units. Much better all-metal units.

Thanks for the watch out reply. Mine is pretty secure from moving around. But I will be keeping an eye on it, especially when I back flush.

My 2016 Arctic Fox TT came with a metal vacuum breaker and a plastic check valve screwed into it, plumbed into the black tank flush line.

However the check valve was installed backwards, cutting off any water to the flushing system. :(

I had to pull the vanity sink top to get enough working room to correct the factory blunder. :M

Keep an eye on it when you flush. I flushed a month ago and afterwards found water under the sink. Ordered a new one off of Amazon and replaced it....no more leaks.

There are 2 kinds of plastic valves...those that leak and those that will leak...as mentioned, securing it seems to increase longevity...

Make sure it is secured to the wall or the cabinet so that it does not flop around while you are underway. Can lead to leaks.

It is a cheap plastic vacuum break valve just waiting for a time to flood your trailer while cleaning your black water tank. Many horror stories surrounding these valves. They make brass ones. Chris

Mine just started leaking as I was flushing out after a Florida trip. I made a note to check it this spring. One of the connections was loose enough that I could turn it with my hand.

And keep an eye on it. They have a tendency to start leaking.

Thanks everyone. Mystery solved.