Grey water tank

1. You don't state year Brand Model
2. Has it drained before OK?
3. IF you are POSITIVE it has at least 10 gallons of water in it and it dribbles, the most common cause is a round 1.5 inch ABS tank hole cut out that has migrated down and is partially blocking the 1.5 inch exit hole. The only way to verify this is to let the tank dribble as long as it takes to stop that dribble. Then you remove the Valve. IF THE VALVE IS CONNECTED TO THE ACTUAL TANK EXIT FITTING. If the valve is downward from the tank in a 1.5 inch ABS pipe, you will have to cut the pipe about 3 or 4 inches from the Tank exit fitting to shine a flashlight up the pipe and see what is blocking the exit hole. Usually, you can use long needle nose plyers or similiar to pull that round plug out. When the OEM's drill out the top 1.5 inch tank inlets on top the tank, sometimes that round plug falls in the tank and they do NOT take the time to fish it out.
4. Last, another common cause is the Valve itself, the rod has disengaged from the knife valve and when you pull the rod or cable the knife valve does not move. When you suspect this (knife valves are cheap), you go to the backside of the knife valve opposite the rod and drill a 1/4 hole in the middle of the valve and take a 1/4 inch rod or screwdriver and push the valve plate open, the tank drains and then you replace the complete valve. Doug

This happened to me and I called the service tech to our site. After a few minutes we realized my Grey tank was full but I was opening and closing the black water tank which was empty.
The valves on my previous trailer were opposite. I realized this when I saw the handle on the Grey water tanks was colored Grey and the handle for the black water tank was colored black.

tbeckley wrote:
Must be a touchy sensor. I moved the coach a short distance & now the gauge reads empty. Thank you for all the responses!

They take a day or so to dry out. The sensors are metal and conduct electric when wet so driving around or right after you drain, they are still wet so still conduct elec.

Must be a touchy sensor. I moved the coach a short distance & now the gauge reads empty. Thank you for all the responses!

Add some cleaner such as Fabuloso, available at Dollar Tree. Get the purple one and add it to the sink water. This will tell you if it's flowing/empty whatever and clean your tank at the same time. You could also add water through your sink via garden hose until the shower backed up and then see if it empties. Gauges don't work very well. I just replaced mine with the SeeLevel system....Dennis

Seattle Steve wrote:
Open the waste valve and run some water from sink or shower. If the water coming out corresponds to what is running into the sink then it's the gauge.

WINNER!

Open the waste valve and run some water from sink or shower. If the water coming out corresponds to what is running into the sink then it's the gauge.

1. Ignore gauge.

2. Open valve. If nothing comes out, it’s empty.

3. If it backs up into shower it’s full.

Check the air vent. Water can't flow without air behind it. It's usually under a sink somewhere.

are you sure the tank is full? Gauges on these RVs are worthless