We have an Avondale osprey 4 berth but have no manual to go with it. Not sure how to fill the spare tank

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

Here are some troubleshooting steps you can try to resolve the problem:
1. Check the Water Pump:
- Make sure the water pump is turned on and functioning correctly. The water pump is responsible for drawing fresh water into the holding tank from an external source.
- Check for any visible signs of damage or blockages in the water pump system.
2. Verify the Tank Fill Valve Position:
- Ensure that the tank fill valve is in the correct position to allow water to flow into the holding tank. The valve may need to be switched from the city water connection to the tank fill position.
3. Inspect the Water Inlet:
- Check the water inlet connection where you fill the fresh water tank. Make sure there are no obstructions or kinks in the hose that could be preventing water from entering the tank.
- If there is a water filter in the system, check if it is clogged and needs to be replaced or cleaned.
4. Test the Gravity Fill System:
- If your RV has a gravity fill system for the fresh water tank, try filling the tank using this method. Pour water directly into the gravity fill port and monitor the tank level to see if the water is entering the tank.
5. Consult the RV Manual:
- Refer to the owner's manual of your Coachmen Elite RV for specific instructions on filling the fresh water tank and troubleshooting water system issues.
I good luck

Possibly find it in a manual

http://www.manualsonline.com/

What is suge? Do you mean Sewage?
Anyway, you most certainly did not hook up to the fresh water inlet properly. This will not fill any tank. Get your manual out and read it.
Contact your local service center directly or online here:

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.

It is likely one of two things, either your RV has a waterline to your fresh water tank that allows you to fill that tank when you are hooked to City water, or the check valve on your water pump is bad and it is allowing city water to fill your fresh water tank. Make sure your freshwater tank is empty, have someone turn the city water on while you watch the freshwater tank... you should be able to see where it is filling from....if it is filling from the water line that run to the water pump, the check valve is bad, if it is filling from a city water fill line, locate the valve on that line and close it. If it is indeed the water pump check valve...you can either replace the pump, or add a cheap inline check valve, like a sharkbite check valve.. they run like 12 to 15 dollars.. install in seconds....you just cut the pex pipe then shove the ends into each end of the check valve.

Contact FoMoCo directly: https://corporate.ford.com/contact-us.html