I'm usually too lazy to bother with repeatedly washing substrate.
I've used this method a few times, and it's always resulted in crystal clear water within a couple hours, if not right away.
I build my substrate with whatever hardscape, terraces, slopes, dirt, etc.
Then I get a spray bottle, and mist/spray the entire substrate for a bit, but not so much that the water level rises above the substrate.
Do my planting, repeatedly misting in between to keep plants moist.
then I'll put down a large filter sponge, and fill the tank (this last time around, I just added water behind a mattenfilter).
I believe the misting/spraying carries the fines down into the lower parts of the substrate, and the sponge breaks up the flow enough that they don't end up suspended in the water column.