Originally Posted by f1100turbo
Attwood - porcelain or glass lined.
Suburban - metal or stainless lined.
The reason that the Atwood does not use an anode is that the tank itself is all aluminum and there is no electrolytic action between the aluminum and fresh water.
The Suburbans (most common) have IRON boilers and are porcelain coated all over the insides EXCEPT around the penetrations (drain port, pressure relief valve, electrical element (if equipped), water inlet and outlet ports). If they ran the glass up to the penetration, it would crack there when the item you installed (with pipe threads) torqued the cast iron.
Without the sacrificial anode, any acidic/basic water will quickly rust/corrode the exposed iron and seal the penetrations in FOREVER. You will need to replace the entire heater if you ever burn out the AC heating element, or need to change the pressure relief valve.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW