Go to the penthouse on top of the Nacht der Untoten building. At the top, look over the edge of the building near the green tarp and you will find a box just towards the left. Shoot it and pick up the flask that is dropped near the water area below.
Once you have collected the flask, look for the nearby tree that is covered in fungus. You will need to lure a Megaton to this area and have it blast the fungus covered tree with its radioactive attack. Having done so, interact with the fungus and place the flask beneath it.
Once the flask has been filled, pick it up and make your way to the Medical Bay in the underground facility. Upon arriving in the Medical Bay, you will find a a small box covered in chains, not too far from the Particle Accelerator door. Using your flask, interact with the box and have the flask remove the chains. When opening the box, you will be rewarded with the D.I.E. Cryo-Emitter.
Once all four cylinders have been risen up, it is time to proceed to the next step