Hydration reservoirs are made by Hydrapack. They sell a cleaning kit that can be found in the link below
If the hydration pack is used regularly, putting the empty hydration reservoir and hose in the freezer between uses will also prevent the growth of bacteria and mold.
The bag itself should be handwashed with warm, soapy water and left to air dry out of direct sunlight. It should not be put in a washing machine or dryer.