My gray water tank won't drain. While washing dishes this morning the sink started filling up. I thought at first that I had left the dump valve closed but when I went to open it it was already open...
I am not familiar with your particular FW, but do you possibly have three holding tanks. Some units have two grey tanks; one for the bath and another for the kitchen.
If you have electric remote operated valves, then you will have to find it. A call to the manufacturer or dealer may give you the valve location.