This is the nuclear option. Turn off the water heater. Drain a few gallons. Pour in one to two quarts of 35% hydrogen peroxide. Let it sit for two hours. Don’t breathe it in—your lungs will rebel.
Fixing the Rotten Egg Smell in Hot Water a Big Bear Guide
Then flush the tank. Rinse. Repeat. The fizzing kills bacteria instantly. It’s like dropping a Pac-Man into the tank to eat all the germs. Nom nom nom.
Tip: Do this outdoors. Your yard will smell like a bleach factory. Your neighbors will think you’re making meth. Let them wonder.