B+ motorhomes

The water tank was the problem in mine. Certain fittings are friction welded to the tank, and if they are not done properly they leak, mimicking leaks from outside. I decided to try a fix, so I drained the tank, made sure it was completely dry, reset the fitting that attached to the leaking one, and then used The best aquarium silicone I could get. After letting it all dry for a few days I tried it and it never leaked after. Sometimes the input hose is not lined up properly, they are usually very cheap like you find on an inexpensive swimming pool. I replaced mine with neoprene hose and used good-quality hose clamps. Hope this helps and good luck!