There is a metal drain plug in our bath that doesn't work very well. It's just a o-ring seal that is supposed to create a seal with gravity, it's not pulled in place by a lever like a sink would be. I'm not sure if the o-ring is bad or if it's just making a bad seal for some reason. Anyways, my question is how to determine the model of this drain/plug assembly so I can order a new plug or just the o-ring? Thanks.