How/where to put hydrogen peroxide in water heater
To add anything to the water heater you will need to turn the water off and drain the pressure in the lines. After this there are 2 choices; Pull the anode probably the best idea because it may have dissolved. The 2nd choice would be to pull the supply line and add there. I have never had this problem that flushing and replacing the anode did not fix. After this purging the air out and checking for leaks when the water is turned on. Just a note if a tap in the house is turned on with both hot and cold water while the system is open water may come out as the cold pressure flows back through the hot line. Had this happen when I left a system open while going to the store to get a new anode, what a mess.