maxilaria,
A trick with washing cc, filter media, etc. is to wash it in the discard water from a water change, IME. You can scrub it, etc. without using cleaners to get it clean enough without nuking the bacteria colonies. Fresh water is not needed for cleaning.
Kiyana,
It doesn't matter interms of settling whether they are on or off, but if you have fish in there, you want them on. Clean the pumps and powerheads part way through according to standard pump cleaning procedures. Good quality powerheads are not harmed by a sandstorm if you put the attachments on to keep very large particles out of the pump. For your fishes' sake, you want the pumps on. However if you add the sand and then put the water back in slowly, the sand storm won't be as bad. Don't try to move the tank part full of water or you may find yourself with a cracked tank, BTW.