just rinse it thoroughly - the water will eventually run clear then you're good to go.
As for dechlorinating it - the relatively tiny ammount of untreated water that the sand will hold will not affect your fish, but if you're worried the just use a dechlorinator in some water witht he sand and just rinse/mix it up like that.
You don't want to add the sand before getting rid of the dust (the dust is what most likely makes it cloudy. - this dust will get everywhere -in your filter, float on the surface, and stick to everything - it will make your tank look pants.
:P
I rinsed my sand in buckets using a hose - standing in the shower cubicle!
