Almost all water heaters have been made the same way for the past 60 years. They construct a steel tank, then bond vitreous glass to the inside of it to keep it from rusting. There are variations in manufacturing quality, however, so some tanks might have a better glass lining than others. And there is always a small amount of steel exposed, due to limitations in the coating process.

To protect that steel, the makers install sacrificial anode rods in the tanks. Click the link for details -- after you've finished reading here. Suffice to say that when your anode is all gone, the tank will start to rust out -- unless you put a new anode in. However, your tank could also rust externally and fail. It has lots of rust protection inside, very little outside, so watch out for leaks. You can see a little of the anode of this old tank, hanging down on the right.

In fact, take a long look at it. There is the white-and-blue shell, the actual tank within it, a flue running down the center, a drain valve (bottom left), a fancy draft diverter, also known as draft hood, on top, with the hot-water outlet visible in front of it. If you had X-ray vision, you could look through the floor and see the gas burner that heats the water and the opening for that flue. It would take more than X-ray vision to see the dip tube because it fell apart long ago.

On newer heaters, though, you would see it as a plastic tube hung underneath the cold-water inlet and extending about two-thirds of the way to the bottom. It brings cold water into the tank to the bottom to be heated.

They tell you to flush sediment, but how can you do that with that flue in the way? (Hint: Follow the link. We show you a way.) Electric tanks don't have the flue, but the bottom is still domed, creating a similar problem. Then there's the straight dip tube that both have. To say nothing of the miserable plastic thing employed as a drain valve. Tiny orifice, occasionally crooked path.

Sediment can be fine sand or big rocks. But getting rid of the sediment is still a good idea. Calcium's good for you, but not for your water heater!