I only started doing all grain about 3 years ago. The technique I've been using from the start was very similar to the original posters outline. However, there were a few times when I rushed the process by dumping in all the sparge water at once and just opened the valve all the way to drain into the brew pot. My efficiency was in the mid 60s on those occasions. But when I kept the drain valve closed a bit and really took the time to match the slow draining with the addition of clean sparge water, the efficiency was in the high 70s and once even topped 80.