Question: When I have water in my fresh water tank and I run the pump and faucets, I see water coming out my city water hook up connection. This did not happen last year. What’s wrong?
Answer: The most likely cause is a bad back-flow check valve. This check valve is there to prevent water that is held in your fresh water holding tank from back flowing out through your city water connection.
You can get one of these valves at most RV parts stores (like Camping World) or a hardware store. As a temporary fix you could buy a solid cap (with garden hose threads) that screws into the city water connection, or use the cover that should already be there to prevent the back flow until you can replace the check valve.
We had a similar situation. We had noticed that our water pump would sometimes cycle on for a couple seconds even when we weren’t calling for water from the fresh water tank. We did some trouble shooting to make sure we didn’t have an internal leak in our plumbing system, and that’s when we noticed the minor leak at the city water connection. So we replaced the check valve.
By the way, the check valve is usually very close to the city water connection – so all you should have to do is take the cover off of the city connection to get to it.
However, you didn’t mention if the city water connection housing was leaking or whether the connection behind it had any leaks. So in the event that it is not the check valve, then you will have to fix the source of the leak. You may need to tighten the connection(s) behind the city water connection housing or replace the housing or fix a broken line to the fresh water tank (hopefully not).