Often it is the tubs. When I buy new plastic tubs, I spray them with bleach and let them set outside. They gather mold in the tiniest of places. Also if I open a container of scraps and they have an odor, since I have prewashed prior to bringing them into the house, I may pitch. I started collecting silica envelopes that come with the different medicine bottles, aspirin and such. Helps to absorb any moisture. With aspirin it helps them from crumbling. They have a moisture absorber on the market at the discount dollar stores. I keep meaning to pick them up but haven't gotten over there yet. My neighbor uses charcoal to put in an old sock or plastic salt shaker. She says it helps when storing in plastic containers. You can use a lingerie bag (I have several) for the scraps when I bring them home and toss into the laundry from estate sales. It is hard to wash out mold. I suggest pitching anything with mold on it.