The house I bought has an acrylic tub that sits on top of an old cast iron tub. The bathroom is on the top floor with an attic above and a kitchen below. Somehow water (not sure of the source) is finding its way between the two tubs. I have caulked and caulked and had both a plumber and an acrylic tub specialist come in and neither knows what's going on. There are no visible water marks or damage above or below the bathroom. Somehow water is getting between the two tubs and only once I unscrew the drain will the water between the tubs go down the drain. Unsure if this is a plumbing issue or if maybe water from outside the house is somehow finding its way in, between the exterior and interior walls, and into the old tub?