I have a mildew odor problem. We have a shower enclosure (fiberglass I thnk). There is a very strong smell of mildew I believe coming from the overflow drain in the tub. I have attached a picture of where I think the odor is coming from. We are only at this house a few days a week so the water is not used for several days. Even after we run the shower it still smells. Any ideas would be greatly appreciated.