It only needs to get exposed minimally to bacteria for it to be a problem. You put it away for later use and the bacteria begin to multiply on it. Just get a new pin. It's not worth the risk.
all I am using one syringe for is withdrawing the gear from the file... i then backfill an insulin pin with it... inject with the insulin pin and throw away the insulin pin... is it ok to just swab the withdrawal needle and recap for later use?