Agreed,just syphon the sand out and into a large enough container.There should be enough bacteria on the inside glass surfaces of the tank to back up the cleaned out fikter for now.If your going to siphon it out i would uses a garden hose. You could aslo net it out.
Dont worry about the bb. Your filters hold most of it. No need to remove it over multiple days. Ive done it plenty of times