check the location of your leaking, most likely the seal on the tub drain is loose and leaking there. you need a tool to remove that drain, let it dry, put on new rubber washer, apply some silicon and re-screw the drain cap up.[/QUOTE
exactly,most of leaking problem doesn't need cut drywall to find out the point of leaking.just go home depot get a special shape tool from plumbing area,open the drain outlet. replace the rubber washer,or maybe use some silicon to make sure 100% water tight.