Hooked up to city water,over nite it filled over flowed the water tank,water leaking on top of the holding tank and now getting a suge smell

no info generic answer check valve - faucet --failure open access and check lines valves pump

if separate fill holes then bad check valve at water pump

Make sure that you hooked up to the right line. Sounds like you are filling the tank instead of pressuring the trailer pipes. Sometimes there is a valve you must close to keep the city water from entering the fresh water tank. If you have your manual, check to see if you did it right.

There should be a diverter valve switch (manual) that allows water to flow into the fresh water tank or supply city water to the RV. Some have a inline 1 way valve that prevents water going to the fresh water tank. When this valve goes bad, water is diverted into the fresh water tank. since it will not allow pressure to build up.

Check to see if you have a valve labeled for tank fill. It sounds like you have a single connection to use city water or fill your tank and it is in the tank fill position. The water you are seeing would be coming from the tank over flow.

Many RVs have the plumbing to fill the fresh water tank from the city water hook up. This valve is usually near the city water hook up and labeling is similar to "city water" and "tank fill". Another anomaly from leaving the valve in the "tank fill" position is that, when not connected to city water, the on board pump may run continuously and the water volume is very low.

Other than a leaking 4 way selector valve the probable cause would be a leaking check valve in the pump.

On the RV the city water and discharge from the fresh water pump are tied together. When on city water the discharge of the pump will have city water pressure on it. If the internal check valve on the pump is leaking, water will flow through the pump backwards and into your fresh water tank.

Typically this requires ether replacing the pump or installing a secondary check valve between the fresh water tank and the pump suction.

it does exactly what it is supposed to do,shut off water when it is full

Probable cause would be a leaking check valve in the pump.

On the RV the city water and discharge from the fresh water pump are tied together. When on city water the discharge of the pump will have city water pressure on it. If the internal check valve on the pump is leaking, water will flow through the pump backwards and into your fresh water tank.