I figured what was happening is the check valve was leaking due to a dislodged worn or damaged o ring.
Rv check valve leaking.
Close all valves then go back inside the rv and add several gallons of water to just one tank.
The valve is designed to let pressured city water enter the rv s plumbing system when hooked to a charged hose bib via your water hose in an rv park and prevent the water pump from pumping water out of your potable water tank onto the ground when not hooked to a charged hose bib.
The leaking issue may be coming from a cracked pipe or a loose connection.
It s hardly an owner friendly arrangement but i have seen it.
Many moons ago the owner of the site called me on a sunday evening to help me.
I bought a 3 years old 5th wheel and found several leaks in the plumbing behind the dividing wall in the basement.
Check amazon or rv water filter store for options.
For those just entering the rv lifestyle there is a check valve behind your city water hook up.
There are worm gear clamps and pex used.
Use good rv anti freeze when winterizing your rv.
If nothing poured out repeat the above steps for.
If you do not want to fool with broken or stuck dump valves.
I had a plumber at home depot tell me you could not use pex clamps on a plastic fitting yet my rv service manager says the rv industry has been doing just that for 20 years.
Inside is a plastic check valve plunger a spring retaining clip and small rubber o ring.
Go whole hog and replace the pump itself.
To determine which valve is leaking you should have your rv waste tanks empty.
If you don t know what you need rv water filter store s customer service is fantastic.
This will help keep the dump valves from becoming sticky after they have sat for a long time.
Wait about 30 minutes then head outside and slowly uncap the waste pipe.
Unfortunately if the valve gets pushed in while the system is pressurized the seal on the valve can get pushed out of place very easily causing fresh water to leak out of the city.
Dislodged check valve seal under the mesh screen in your city water inlet there is a little valve that is meant to prevent backflow when using your water pump.
An occasional rv will be found that has a 3rd dump valve and even 2 separate dump hookups.
With the wastewater valves closed and the black cap off place a 5 gallon bucket under the sewer drain port.
Our city water connection has been weeping water when using the onboard water pump and fresh water tank for dry camping.
Did any water leak out.