Can someone identify this for me?

Test your black tank flusher and watch that valve. Ours is in the bathroom cabinet under the sink and was exactly that same black type. It leaked the first time I used the black tank flush and put water all over the floor. It got replaced under warranty with a clear plastic version that seems a little better quality.

I work with enough plumbing to understand what it was as soon as it leaked and really got a laugh out of the dealers reaction when I told them what happened. I got the canned answer "We're not sure what's going on....We've never seen that before!" LOL....really?....