Although many organizations such as the NSF (formerly the National Sanitation Foundation) warn against re-using food storage containers, it is possible to sanitize them so that they’re safe to use. For instance, soaking containers in bleach water and then washing them either in the sink or dishwasher can disinfect them for re-use.
One tip for safely reusing food containers is to check their ratings. For instance, recycle containers that are not rated dishwasher and microwave safe. Also check their condition before reuse, and recycle containers that have started to bubble or warp; this means the plastic has started to break down, and they won’t seal tightly.
To disinfect used containers, especially those with stains, first soak them in bleach water, which both lifts the stain and kills bacteria. Then, wash them in the dishwasher or sink in hot water with anti-bacterial detergent or dish soap. Let them air dry, and if at all possible, dry them in the sun to disinfect even further. Doing so every time you wash used containers means that they may last for more uses.
Commit yourself to recycling a few used containers each time you eat leftovers, even those made by companies such as Tupperware, Glad and Zip-Loc that are meant for limited re-use.