There would be time for him to come back and dispose of it properly later.
"Have all the people who participated in the event been properly disposed of?"
The groups are required to properly dispose of the needles.
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They must be properly disposed of and handled according to the instructions.
"Is there someplace where I can dispose of it properly?"
Make sure you dispose of them properly - which means no more flushing!
Furthermore, in many places, failure to properly dispose of a body is a crime.
You fear it may never be properly disposed of?
Instead, they will have to be properly disposed of on the spot by authorised companies.