Eli5 when it’s windy outside why does the water in toilets swish a little bit?

Question

Eli5 when it’s windy outside why does the water in toilets swish a little bit?

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Answer 1

When the air pressure outside is unsteady, the entire plumbing reacts to that change. Specifically, when it’s very windy the air pressure outside is lower, which causes the still air inside to push the water more and cause movement.