Atwood water heater tanks are Aluminum Alloy (No Anode Rod----Suburban uses them)
The tank should be flushed/rinsed routinely to get rid of scale/deposits...but with only a 1/2" hole it can be tough to get crud out.
With water supply OFF, I relieve pressure (open hot faucet) and then remove drain plug. Then I turn water supply back ON (faucet closed) so that full water pressure blows out drain hole. Cold water inlet dip tube points downward so it helps stir up any stuff on bottom of tank.
After blowing I then turn off water supply.....open water heater T&P Relief vlave and drain WH tank. Then using a 'wand' (get them at most any RV store) that goes on end of garden hose I stick it in tank, point it up and blast away top/sides and as much of electric element as possible.........then drain.
Close T&P Relief valve open water supply and let it rip again.
I do this 2X a year.
Water source in S.Cal is HARD so deposits are normal.
Did you find your tank capacities?
HERE is some info...if it's your model
