our water heater is 15+ years old, never been flushed, but is protected by a whole house rust and sediment filter. accoding to this website http://www.waterheaterrescue.com/ , the home owner can do a number of things to the water heater befoire installation that will greatly extend the life of the water heater. their main claim is that a good quality heavy duty sacrificial anode will make a 6 year warrenty heter perform as well as a 12 year warrenty heater. what are your thoughts on their claims about the sacrifical anode? do you now any plumbers who can verify these claims? thank you.