Here's a photo of my convenience center:
If you notice, I attached a green (short) garden hose to the black tank flusher and I just leave it there permanently. So, when I run my black tank flusher, I can just connect the hose to the green one already there.
Why? First, connecting hoses to the inlet on the camper is very hard, because of it's location. Second, when connecting at the inlet, it often leaks. It's hard to get it tight so water does not spray everywhere. Third, the inlet on the camper is a soft plastic, and easy to cross thread or damage with repeated screwing on and off wearing down the threads.
By attaching another hose, it saves the threads on the trailer connection, and then when I disconnect, the water that back feeds under pressure can be drained outside the convenience center by simply lowering the hose. I keep it there permanently. It's never been taken off since I put it on there.
Also, this is a very, very easy way to run the black tank rinser when there is no shore water available. Simply connect that blue hose for the shower to the garden hose, and turn on the shower. This works very well, as almost always, the hose provided at dump stations is way to short to reach the front end of the camper and the black tank outlet as at the end of this 41 foot behemoth.
It's an easy solution .... IF you can find a short garden hose. I think the one in the photo is 5 feet.