Washer fluid bottle cap

[D&D]

Has anyone else come up with a better solution for a cap? I went to add washer fluid when I was working on the intermittent wiper project. The factory cap disintegrated when I removed it. I suspect the plastic is not uv resistant.

expandable rubber plug or test plug.
hardware or plumbing store would have them

Expandable Rubber Plumbing Plugs | T-Handle Expansion Plugs

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