My sacrificial anode is leaking - Rheem Water Heaters

A sacrificial anode is usually made from magnesium, aluminum, and zinc. Magnesium has the most nutral electropotential of the three.
Boats use copper sometimes.

All water heaters that have storage tanks have what are known as sacrificial anodes. These generally last the life of the heater, but in cases where the water is excessively acidic, they may need to be replaced after a time.. Otherwise, I wouldn't worry about it.

no
try contacting the manufacturer for the part or talk with a plumber supplies shop ( where plumbers get their supplies and parts ) to see if it is available
it will be a sacrificial rod to prevent the tank from corroding out especially around the heating element fittings

There is a "sacrificial anode" inside of a hot water tank, electric or gas-fired. Its purpose is to corrode at a high rate, in order to protect the rest of the heater from corrosion,

All hot water tanks (save the plastic ones)corrode. It is a given,

The sacrificial anode is usually made of zinc, or a zinc/copper/other alloy. When it gets eaten away from electrolysis (the action of minerals in the water, and the metals components of the hot water tank/heating elements/etc make the entire unit operate as a small battery), it usually turns a nasty, crumbly black.

It will leach into the water, and if enough chunks fall off the anode, it will color the water as you describe.

The SOLUTION, to "FixYa", is to write down the model number of your hot water tank, go to the local Home Improvement store (or Amazon.com) and order a new anode. Replacing it is pretty straight-forward: turn off the water, turn off the heater, drain the tank down a bit from a faucet that is lower than the top of the tank (or the valve at the bottom of the tank) , remove and replace the old anode with the new one (it screws into the top of the tank, and is a large-headed "bolt", maybe an inch-and-a-quarter across).

Now that I have written this tremendous missive, I re-read your question/problem and see I missed the mark.

You have "black water" backing up into your shower.

You've plugged your sewer line a bit. Quit using so much toilet paper, you have a near-stoppage of your line. Pour a bottle of Liquid Plumber (or two) down the shower floor drain, let it sit for a number of hours, and then run hot water down the drain at as fast a rate as you can before it starts backing up to clear the clog.

Your use of the term "black water" makes me think you might be in a RV (Recreational Vehicle) or the like, so your problem may be cold-weather related. A heat-gun or hair-dryer ran along the drain lines (or a big heater aimed under the RV for a while) might unfreeze the clog and allow it to pass into the holding tank or sewer line.

Your "Black Water Tank" may simply need to be emptied, too.

Flush more often (important!), use less paper in each flush, eat less beans, and try to p**p in the RV public restrooms more.

Even so, if your are in an RV, the sacrificial anode in your hot water tank is good for only two years, tops, before it fails and your very expensive hot-water tank starts to leak. Fix it anyway.

As soon as you pull out the anode rod(and not put it back) the walls of the tank will begin to rust. The sacrificial anode is there for a reason. If it's eaten away, replace it. If it's totally gone, the tank has been being attacked for a while and might be due for replacement.

replacing the anode will increase the life of the tank. it is the large nut on top of the tank. it is a sacrificial material that helps prevent tank rust through.

This model has one sacrificial anode, located underneath a plastic cap. Drop water pressure, unscrew anode.
It's long. There are two types available, magnesium and aluminium. Replace like for like.
Magnesium is for soft/treated town water, aluminium is for harsher water.
The condition of the anode you take out will tell you if you timed it about right.
Needs doing every 5 to 6 years, along with the relief valves.
Mine was made in 2006, about to do this job for the second time.

The proper term is a "sacrificial anode." The idea is that it is made of a softer attractive metal for corrosive minerals. The minerals attach and destroy the anode first before the tank. You should inspect the anode at least once a year.