Waterproofing toilet

Hi! I have a laundry room in a Strata complex which I want to turn into a toilet room. No shower, just WC and existing laundry tub. A core hole is required. Under me are garages and plumbing are easily accessible. Given a core hole will be done, do I have to re waterproof the whole floor which means ripping up the tiles, waterproof and re tile? Or a sealant around the core hole will be enough to comply? Thanks a lot!