You need to sanitize it before use, yes, but if it is clean, then you don't necessarily need to sanitize it until the next time you use it. Store it clean and dry.
HOWEVER <---- BIG HOWEVER
Never never never use dish soap or soap of any kind on your brewing equipment. Soap is the bane of beer. It will ruin your head retention. Anything that touches soap will need to be rinsed one zillion times.
When you're done with a carboy, rinse with water, then scrub remaining crud with your carboy brush. Rinse more. Then fill it with water to soak. Then after a while, scrub it again. Never use soap. Water and elbow grease. MAke it immaculately clean, dry it and store it. Then be sure to sanitize it next time before using.