In order to do it take a bottle (not glass) or other container in which the reaction takes place, provide it with an exit pipe (it might be easy to arrange it in the cap), run the pipe in another bottle (any material) straight to near the bottom, provide that second bottle with an exit pipe near the top , fill it up to 3/4 with water in such a way that the pipe coming from the reaction bottle is submersed and the exit pipe is not.
When the reaction produces hydrogen the pressure developing inside the container drives the gas to the second bottle where it bubbles from the bottom to the water surface leaving behind most impurities, the pressure developing inside the second bottle will drive the hydrogen in the exit pipe.
Provide that exit pipe wit a T junction where at one end there is a balloon acting as pressure tank and from the other end you can inhale the hydrogen, a valve will enable to regulate the desired pressure/gas flow.
An oxygen canula should be extremely cheap or make your own with a couple of T junctions and some pipe, connect it to the valve and you are ready to breath quite pure hydrogen, easier done than explained.
Beware that the lye/aluminum reaction develops heat which can melt the bottle if it is a plastic one, in order to avoid that keep it in a bigger water container as a cooler.