After your done rinsing it with either Ro/Di, or treated tap water as stated above. Make sure you do a final rinse with salt water at the correct salinity. I added a bunch of sand a while ago, making sure that I rinsed it really good. When I added the sand to the tank, I forgot about the added freshwater. Luckily, I only added a few pounds of sand, but my S.G. went down pretty quick.
or
You could just wait till it dries out before adding it.
