Found this, no personal experience with one though. Just wonder what the odds of getting the old one out without starting a leak or twisting the end off.
Water Heater Anode Rods - Additional Information
Aluminum Anode Rods - Least expensive of the anode rods we offer and normally corrode at a slower rate than other anode rods. Most water heater manufacturers install these in their water heaters as standard equipment.
Magnesium Anode Rods - Normally corrode at a slightly faster rate than most anode rods, but dissolved magnesium in water can offer many health benefits.
Aluminum/Zinc/Tin Anode Rods - This combo rod is designed to fight some foul water odors that can occur in water heater systems that use aluminum or magnesium anode rods. Please read our FAQ for more information regarding water odor.
Hot Water Outlet Style Anode Rods - This style of anode rod installs into the hot water outlet of the water heater and yet allows the water to still flow through the outlet. These allow the installation of an anode rod for those instances when the normal anode rod has corroded too much causing the steel to rust or corrode in such a way it is now impossible to remove the old rod. Or, for those who just wish to add a second anode rod into the water heater for better protection. Please note: Some water heater hot outlets can have a calcium build up inside the outlet, or the tank may have not been properly bored out underneath the outlet opening, possibly causing interference with this rod slipping into the water heater.
Hot Water Outlet Aluminum/Zinc/Tin Anode Rods - Contain a built-in heat trap nipple with a fluoroplastic ball that sinks inside the nipple, into a seat, as water flow stops. This is designed to keep any cooling hot water from entering back into the water heater potentially cooling the water heater down. The seat is equipped with a safety relief port. When water is not flowing, heat is effectively trapped in the water heater reducing standby heat loss.
Hot Water Outlet Aluminum Anode Rods - Least expensive of the hot water outlet styles, this particular anode rod has a built-in dielectric nipple (no ball or seat) allowing less water restriction than a heat trap nipple.
Flexible Anode Rods - Used when access to the top of the water heater has limited clearance due to any obstruction such as low ceilings in closets, attics, under stairwells or in basements. The anode rods are manufactured into three or four sections connected with a solid steel wire or stainless steel braided wire. The Flexible Aluminum Anode Rod has three sections of aluminum attached to a solid 1/8" low carbon steel center wire core. The aluminum will corrode and disintegrate before the steel wire can. The Ultra Flexible Magnesium Anode Rods have four sections of magnesium on a steel rod. The sectional connections are made with copper couplers and 301 stainless steel braided wire providing greater flexibility during installation.