I used 3 bags of fluorite black sand in a 25gallon. I lightly rinsed the bottom two bags, and I rinsed the hell out of the 3rd bag and used it to cap the mildly washed stuff.
The tank still got cloudy when filling up, but settled in a day, and I have no issues a year and 2 major rescapes later. When my cories dig during feeding time they stir up a slight grey plume of dust that dissipates quickly.
The general consensus from all of my reading was wash it all, but it wont get 100% clear. The water pressure from the hose or whatever will knock some particles off of the clay pieces and make the water cloudy. You just want to get the water running off from your bucket to 85% clear and then move on.