A water tank overflow dechlorinating assembly is used with a water tank including an overflow pipe with exit above an overflow discharge region with an air gap between the two. The assembly includes a dechlorinating material delivery assembly comprising a guide tube having a material supply region and a perforated region positioned within the air gap. Overflow water passes through the perforated region for interaction with dechlorinating material therein. Depleted dechlorinating material within the perforated region is automatically replaced by dechlorinating material from the material supply region. A weight can be used to bias the dechlorinating material within the material supply region into the perforated region.