A drainback tank requires no maintenance.
Although drainback tanks aren’t typically lined, they also aren’t subjected to the corrosion-causing daily exchange of oxygenated water that water heaters and storage tanks endure. An important service check with drainback tanks is ensuring the water level is sufficient to cover the exchanger coils. As with many specifications for SWH systems, a difference of opinion exists on what to use for the heat-transfer fluid (HTF) in a drainback system. My company always used tap water, but some installers use distilled water.