Problem solved thanks to the RV Proctologist. They attacked the tank from the drain side with a 3000# pressure jet and totally destroyed the blockage. (I'm thinking I helped loosen it with the enzyme stuff???) Anyway, it's now working perfectly and my tank is as clean as new. While they were here, I had them do the black tank also and they threw in the hot water heater while they were at it. So now, all my tanks are as clean as new.
The pressure jet broke through almost immediately and the tank started draining with big black chunks coming out. They pressure washed the tank for about 20 minutes until the water ran completely clear. Excellent work, if you're ever in the Lake Havasu area, I'd recommend these guys to clean your tanks.
Also told me to NEVER use Rid-X in an RV tank, it destroys the drain valve rubber seals... Just use the Enzyme cleaners about once every 3 months or so to keep the tanks clean.
Thanks again for all the help!!
Loren