As said above, put bleach into hot water tank, as much as possible. I pour it into the drain on the HW tank. Fill it up with water, let sit for a day if possible, then run it through your water lines, including outside shower. Empty the tank, fill it up, drain and then fill it up again. Run fresh water through the water lines also. I would also recommend putting bleach into your water hose that you use for city water hook up.