If I could make a suggestion---can you get some pictures up here of the areas and issues you're trying to fix. "handle under the slider by tires black handle" is pretty descriptive but that handle could be for any type of use and pulling it may or may not be connected to your leak problem. I'm guessing it's not since you stated that the leak occurs when the faucet is used and there is water pressure in the shore water hose. This indicates a leak in the fresh water supply piping rather than a drain issue but that could also be your problem if the tank is full. Have you recently drained the waste tanks or are they permanently open to a fixed drain?
