don't actually drain the tank. leave the water supply on so that the pressure will help blow the sediment out. If it does actually flow out, wait about 5 minutes, carefully check to see if the water coming out of the hose is hot, if it's not hot, let the water flow on your hand and feel for sediment grit in the water. Once it feels clean, close the valve and repeat next year. If there is rear access to your tub valves, the new installations shouldn't be more than a couple hundred bucks a piece (plus fixture).