I'm keeping fire eels in the tank, which is why I wanted the soft sand. The extra fine is pretty silky smooth (hopefully this won't end up being a problem). I am using a sump and there are three compartments that are separated with baffles, and there are sponges between each one. I wouldn't think any of the sand would find its way through to the pump impellers, and hopefully it doesn't.
I'm working on washing it now. I'm just filling a five gallon bucket about half full of sand and then run the hose full blast down through the sand and let it overflow out of the bucket for a little while. Then I dump the water out, refill and dump it again a few times. This seems to be working pretty well.