While flushing the black tank on our Bighorn 3055 my wife noticed water on the floor near the entry door. The pool of water got bigger the longer I flushed the tank. I immmediately shut off the water supply and removed the curbside access panel in the basement to expose the plumbing and electrical components in that location. Water was found to be leaking from a supply line to the black tank only when the water source to the flushout was turned on. As the water pooled on the floor in the access area it made it's way under the wall in the fuse and circuit breaker area were we could see it on the floor. The line that is leaking disappears up the curbside wall into an area completely inaccessable without removing a panel from inside the small closet by the front wall and maybe not even then. Has anyone had this happen and does anyone know where this line terminates? And why does it go up the wall and not down toward the black tank? When the system is pressurized for normal use the leak does not appear with or without water running.