To completely seal off a bathtub overflow drain—often done when using a specialized deep-bath cover accessory—you can attach a suction-cup overflow sealing cap over the faceplate. If you need to seal it permanently due to a plumbing renovation, you must remove the faceplate, disconnect the internal pipe, and cap the sanitary tee behind the wall. Callout type="warning" title="Hygiene Warning": Never permanently seal an active bathtub overflow without providing an alternative drainage path, as unattended filling will cause catastrophic flooding. Verification: Test the seal by filling the tub and confirming water does not leak behind the wall.
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