At most of the places I dump I don't think the hose would fit down the hole easily. The end of it that connects to the camper would hang up. At least for a second and give you a chance to grab it. I think it would take work to get it to go down the hole.
Come to think if it, most of the dumps I use have a elbow in them just below the ground. Maybe this is part of the reason why.
When I camp where there is a dump port at my site I don't even leave the hose hooked up. I just use it when i need to dump and then put the hose back in the bumper.
Tennis balls being dropped in by little kids sounds easy enough though.
