Tinovack - I've done this MANY times. First, fill your fresh water tank about 1/3 full BEFORE you add any bleach solution. If you don't, most of it will go into the hot water tank which fills first. Then, mix the bleach with about a gallon of water and put it in. Finally, fill your tank the rest of the way with water. Let it sit as long as you want.
When you are ready to clean this out, run it through the sink and toilet faucets until the fresh water is empty. Do this using BOTH the hot and cold faucets! This will clean all the piping, AND your drains. It will also freshen your black and grey water tanks. Empty them, black water tank first.
Next, refill your fresh water tank and again, run BOTH the hot and cold water until the tanks are drained. This step is necessary to remove the chlorine taste from the fresh water tanks. Drain the black and grey tanks again.
Finally, you can fill the fresh water tank to the level you prefer and you're ready to go.
- Jack