The issue we came across was with the customers Suburban water heater. We noticed some corrosion on the anode rod / drain plug. Having some extra anodes with us, I offered to replace it.
As you can see from the pictures, the anode rod was completely used up, allowing for corrosion to be directed to the carbon steel water heater tank. It is important to, at a minimum, to check your anodes on Suburban water heaters annually, or every 6 months if possible, and flush the tank out and replace the anode if necessary.
**Note** It is important to flush your tank annually regardless of brand, however, the anode system is only used in Suburban water heaters. Atwood tanks are made of aluminum and will not corrode.