Yes, you can put milk into Chilly's Bottles. We recommend a really thorough clean straight after use with hot soapy water. For further cleaning please use bicarbonate soda and water.
When not using your bottle, we recommend storing without the cap on to allow the inside to dry out.
We do advise caution not to leave any organic products such as milk or orange juice that can spoil in the bottle for too long as this may cause pressure to build and potentially damage the bottle and lid.