Are there still flies in them? If so. Use them till they are all out. I like to let the maggots use up most, if not alll the media . Then I let it dry out a bit. Make is easy to shake out the old stuff , so I can wash and reuse the cup. If you buy new cups , then you can just toss it out . I always try to spray the culture with a bleach solution to kill anything living in the culture before I toss them out.
Hope that helps .
PS: Next time try posting related topics in related sections . Might help with faster responses . This might have been better placed in "food and feeding". Im also new here . Welcome.