Sandro,
I am not familiar with the plumbing of your coach, but if the tubing is indeed soft rubber (what you call 'gum') then it most likely is just an overflow or drain and not a pressurized pipe...is the water coming from an open end of such a tube, or is it in the middle of a run? How much water is involved -- much less than a liter, much more, or continuous?
Are you presently connected to a shore water supply (via garden hose connection) -- I ask because there is a check valve in the water system that keeps the on board fresh water tank from filling when you are using external pressure water. If that check valve seeps a bit, over time the fresh water tank will fill to overflowing.
A picture of your water leak and its source will help members here with your model coach better address your issue.
If it is a small fresh water leak associated with being connected to external pressure water, it should stop when that water is shut off. It is a good idea to use a pressure regulator to keep the pressure in the coach plumbing under 40 to 50 PSI or so, and small in-line regulators are sold in RV supply stores for just this purpose:
http://www.campingworld.com/browse/s...FUVhfgodNQYHJg
Enjoy your upcoming trip!!
Chuck