Get under there and see where it’s coming from.
that’s enough water that you should be able to follow the drip
Does your fresh tank fill while you are on city water? If it fills for no reason, maybe the check valve on your pump is bad?
When you run off your onboard tank, do you hear the pump randomly turning on even when nobody’s running water? That’d be another sign that its a faulty check valve.
Go look
Are you in an area that freezes? Afraid the only answer may be to crawl under and follow the drip.
I didn’t see any mention of a water pressure regulator on your hose.
You might have to manually inspect your plumbing. rodents might have chewed through the plumbing. It has been sitting for 2 years
Source: Puddle forming under Travel Trailer, only happens when connected to city water, info in comments
