I am pretty sure a baby bottle has been used to hide drugs in. All you would need to do is find a liquid proof long cylinder that would fit into a baby bottle. Glue the cylinder to the inside bottom of the baby bottle. (long cylinder inside long baby bottle) Put your stash into the inner cylinder - screw the inside liquid proof cylinder lid on - fill baby bottle up with milk (thus hiding the inner liquid proof cylinder) - put the lid on the baby bottle. When you need your stash - just empty the milk and unscrew the inner cylinder lid. The inside cylinder could be as small as 5/8" or smaller in diameter.
Amazing!