I shall refrain from childish name calling. As observed by John the post contained insufficient information for anyone to help you.
If you plan to use a mains supply regularly, it would probably be better to convert the system to something such as Whale. This would allow you to draw from the waterhog, or the mains. The mains in turn can be via the Whale Aquasource system, or controlled by float in the hog. You can also fill the onboard tank via mains and then use this tank as you do now if preferred.
Since the plumbing and wiring are presumably already at the caravan wall, this would seem a reasonable solution