What actually works to drain a hot water heater?

Power off first (or gas to pilot/off), then close the cold supply valve on top. Give it a few hours to cool unless you want scalding water through a hose. Attach a garden hose to the drain valve near the bottom and run it outside or to a drain lower than the valve. The bit people miss: open a hot tap somewhere in the house so air can get in, otherwise it drains at a trickle. Then open the drain valve. On an older tank sediment can clog the valve. Briefly opening the cold supply with the drain still open stirs it up and pushes it through. When you refill, keep a hot tap open until it runs steady with no spitting before you switch the power back on - an electric element run dry burns out.