I just replaced the anode rod in my suburban tank today. Wow, was I surprised by it's condition. I've only had the RV for about 3 months but I don't think it was changed in a long time. The rod was almost completely gone. I also purchased a flushing wand to rinse out the tank. That was a great investment as I spent about 20 minutes flushing out all kinds of "gelatenous" white stuff. At first they looked like white rocks, but they were squishy. It took alot of washing, but it is finally clean. And the best part, the heater seemed to heat the water up much faster once it was clean.
If you haven't ever used a flush wand, try it. You would be amazed at what comes out.