If you wanted to use the sand right away, you would clean it with saltwater to keep it “live.”
But since you are knocking the tank down for a later setup, wash the sand with freshwater and dry it out. I have done this by filling a five gallon bucket about half way and sticking a hose into the bucket and using it as a mixing stick while the water is running. Allow the dirty water to overflow the bucket until you are getting clear water. Keep on doing half buckets until all the sand is cleaned. I dry the sand on a 3.5’ x 3.5’ tray I picked up at a scrap yard….stainless steal that supposedly came from a pharmaceutical company.
When you are ready to use it again, either seed it with a cupful of sand from an existing tank or use a product like Bio-spira, or just let it seed itself with the cycle and live rock you are putting in.
On another note, you didn’t mention live rock. If you allow this to dry out, it will need to be cured again. I would rinse the rock very well and cure it in its own bucket with multiple water changes…you wouldn’t believe the nasty smell it will give off. I would not recommend curing in the new tank. You get a tremendous ammonia spike and again, nasty smell.