Coffee Appreciation

I drink from the "lower lid", as it were.

You do have to have both on but you could equally take both off

So what you're saying is I have to have both on but could equally take both off?
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To make it more clear (finally found a picture that shows the thing)

You say you can drink nicely from the dark (plastic) thing?

One can also remove this and drink from the white (metal) bottle?

Can one leave the plastic thingie at home and still be able to close the bottle tight or does the plastic bit act as a "seal"?

Thank you!
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