Minecraft wiki entry for Elevators, associated text: Once you are at the intended top of your elevator place signs two and four blocks below your feet. You cannot reach down 6 blocks so now you can start with the water sources. Put one on top of each sign, then ready your signs, more full buckets, and jump in. Use the swimming action to stay in the bottom-most water block and place signs further down the shaft, then place another water bucket above this last sign (depending on the size, you may have to keep returning to the top to reload your buckets and repeat until you get down to the bottom).