Add water to the new tank, move rock to the new tank, gravel vac the sand with the water that remains in the old tank. Move sand to new tank. There are tons of beneficial things living in the sand beds, such a shame to rinse and kill it. Never place your rocks on top of sand, always lay the rock down first directly on the glass/acrylic. That way, things that start digging in the sand dont cause shifts in the rock work.