6. Flimsy Plastic
You can put plastic into the dishwasher only if it is reusable. Otherwise clean your plastic containers and plates by hand. If there is no special warning or sign, simply do not put the thing into the machine. There are a few brands like Tupperware that manufacture plastic items that can be washed in the dishwashers. If the plastic is very soft and flexible it may just melt in the device.