Alan, my Atwood aluminum tank corroded out, and the new replacement didn't have an anode. I purchased one from the local RV supply store. It replaces the drain plug. There can be stray electrolytic currents if the sediment in your water contains metallic ores, or there is contact with any steel parts of the trailer. IMHO, an anode is an inexpensive way to lengthen the life of the tank. Beyond that, you need to blow out the sediment which forms at the bottom of the tank, below the level of the drain plug. You can buy a curved tube which fits on the end of a water hose. This is also available at RV stores. You run the water through the hose at full pressure while the tube is inserted through the drain plug hole. Waggle the tube through 360 degrees , and keep it moving for a couple of minutes. With my tank this shifts some nasty grunge. The other task is to keep the burner tube clean. The tube is removed (mark the place on the slider so as to reassemble it identically), and cleaned with a "bottle brush", again a specialist tool from the RV store. I also use a brass wire brush on the thermocouple to remove any carbon deposits. Have fun! Nick.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."