Diatomite Toothbrush Holder

The diatomite toothbrush holders become dirty with yellow and black mold. I guess the water sits in there after you put your toothbrush back in. Does not absorb and dry like advertised. I've attempted to clean it out with vinegar, baking soda, and scrubbing it and it won't come clean. It's also darker than the ones I haven't tried to wash, which tells me it's REALLY retaining water.