How to join PVC pipe in a food safe way


I want to close a rectangular vertically mounted pipe with a piece of flat PVC plastic.
I will use the pipe for growing herbs on the wall outside my house, so it needs to be non-toxic.

I was thinking of using glue or cement for that. Does anyone know any non-toxic glue or cement to do the job?

Or maybe someone have a mechanical idea without using glue?

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