As GeorgeRa said, might not have an anode if it is an Atwood, but to my knowledge all Suburban models have and anode that serves double duty as the bottom plug. Even if the anode was fully depleted (as mine was neglected by its' former owner), there should be a thin rod on the plug that never dissolves.
There are magnesium and also cheaper aluminum anode rods for sale. I buy the magnesium as we have very hard water and it is better at "doing its' thing".
While you have have the rod out, flush the tank out to remove any loose deposits. I use this: