It's actually pretty simple. Fill the bottom of a 5 gallon bucket - about 1 gallon's worth of sand. Put a garden hose into it, and while it's filling, just keep swirling around the sand. The larger bits will sink faster and the lighter bits (dust, etc.) will stay in the water column for longer. Pour out the top water, and repeat. Do this until the water is running out clear. (One step that I took that I believe greatly helped me clean the sand quickly was to pour the sand into the bucket from a height of about 4 feet, with a slight wind blowing. The wind blew a lot of the dust around before it ever even got to the bucket - again the larger bits will fall into the bucket while the lighter bits will be pushed aside by the wind.)
I just added sand to my tank (picture in sig) a few days ago and each gallon of sand only took about 10-15 minutes of swishing - maybe a little less. I also left the tank full of water when I filled it, but poured the sand into place slowly with a small pitcher. This allowed the sand to take a more natural looking place in the tank, and I could easily adjust how much sand was being added to any given spot. This clouded up the water a bit at the end (primarily, because I added large rocks after a while and used the sand to hold them in place, and I was dropping the sand from a much higher distance). The water cleared up by morning (I did rinse out some floss in my filter after about 2 hours, and again in the morning and once more by the following afternoon).