With your taps inside and out all shut tight, and the safety valve not opened either, when you take the plug or anode out the water should just gurgle out. I have used a toothbrush through the hole as it's gurgling to stir up the sediment and cleaned it out pretty good. Also putting a wand onto your hose, soft plastic would be good, and putting it in through the drain hole while running water into it.
A lot of the sediment comes from the anode. If you don't have an anode, likely there will be very little inside to worry about.