I use 1-1/2 cups of Clorox to a full water tank twice a year. I follow the method that Powderman states above. Turn on every faucet until you smell bleach, then let it sit.
This is the detailed method I follow:
1. Open the pressure valve on the hot water heater.
2. remove the drain plug on the hot water heater and drain completely.
3. Put the bleach in the fresh water tank.
4. Put the HWH drain plug back in and close the pressure valve.
5. Turn on the pump and let the HWH refill.
6. Open the faucets one-by-one starting with the farthest from the pump.
7. When you smell bleach, shut off the faucet and move to the next one.
8. Wait several hours.
9. Drain and refill the fresh water tank.
10. Drain and refill the hot water tank as described above.
11. Repeat the faucet exercise until you don't smell bleach.
11. Then, I repeat steps 9-11 one more time.
By this time, I usually can't tell whether there is a bleach smell or not, so I have the DW come in and check each faucet to make sure it smells bleach free.
