Black Tank Flush — Water Drains From BTF Inlet

[DCB]

I have a built in black tank flush (BTF), and I believe it works properly. However, when I disconnect the hose from the BTF inlet, there is always a substantial amount of water that runs out of the inlet into the convenience center and onto the ground — or onto me, if I don’t get out of the way. Is this normal? I haven’t found any other comments referring to this.

After researching, this is my guess — the water is what was in the line up to the back flow preventer under the bathroom sink. I guess there’s nowhere else for it to go but to run back out of the line.

Am I on the right track? Anything to worry about on this specific issue? (I have read other threads about eliminating/replacing the back flow preventer, and I will probably do that at some point.)

Thanks in advance.