I have at least three leaky sinks and they seem to all have the same problem- they have metal down pipes from the drain that mate to PVC... and they leak where the material changes. It looks like they have a washer that fits tightly on the metal and a plastic collar that slips over the metal and washer and threads onto the flange which is the plastic. Is something missing here? Should I change out the PVC for metal? Any ideas are greatly appreciated. Note this affects a kitchen sink, at least one bathroom sink and a utility sink. Thanks everyone!