How do I block a hole in the wall temporarily from mice?

I have a hole in the wall under the kitchen sink where the water and drain join in with the bulkhead that is used for utilities. I have a mouse that I believe is getting in here. Since it's an apartment and the access is still required I can't block the whole permanently. How can I block it temporarily? See... show more I have a hole in the wall under the kitchen sink where the water and drain join in with the bulkhead that is used for utilities. I have a mouse that I believe is getting in here. Since it's an apartment and the access is still required I can't block the whole permanently. How can I block it temporarily? See picture for more details.
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