Hi i dont think there is anyway to completely remove the yellow stains unfortunately
Boil water adding pinch of baking soda... Then pour in plastic boxes and keep it for 10 mins... Clean it and then place the boxes in sunlight for 3-4 hours... 95% uellow stails will be gone
Applying vinegar and salt and lemon to plastic container an bottles will remove the stains and odour from the containers and bottles one tbsp vinegar juice of one lime and one tsp salt mix and apply to the containers and leave it overnight....wash eith liquid soap in morning....
U can keep them in sunlight for few hours...stains will go away. It is tried and tested formula