I usually fill a bucket about 3rd deep with the gravel and then use my hose on the jet setting. Keep the bucket tipped over slightly so it does not fill up (i.e. just overflows on one side) and when the water get really murky give it a tip to get rid of the water. Keep going until the water is clear. The trick is the tipping rather than just relying on the water overflowing - it gets rid over large volumes of muck in one go rather than leaving in the gravel to get mixed back in with the gravel.
I've washed lots of gravel over the years...
Gravel Geek.