You clean out the salt with lots and lots of water. If it is not salt, but scale - calcium and other minerals etc - there are several aquarium safe products to help with that(until I dig for the cheap diy methods). However, with any used tank, disease is a much greater problem than salt, which is not an issue(see below). You should disinfect the tank and ALL associated equipment decorations and maintenance accessories. DO NOT USE SOAP-very toxic to aquatic life and too tragically easy to leave residue. You can use plain(without detergents etc)chlorine bleach-but make sure it is well rinsed very well, and I also use a chlorine neutralizing water conditioner afterwards just to be sure. Or to disinfect more safely, you can use... LOTS OF SALT! Think 'Dead Sea' here. I almost make a paste of it. Accidently left over trace salt will not hurt any freshwater set-up. In fact, except in the case of the few salt sensitive species, salt(NaCl-no additives, iodine, etc.) may be dosed medicinally to control many parasites, etc., or alleviate nitrite poisoning (second stage bio filter cycling). I have used salt with my goldfish. www.youtube.com/thecuddlefish