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?

In: 1241

Answer 1

[The vent stack is open to the sky](https://i.imgur.com/U2RmGwF.jpg). Its primary purpose is to break siphons so draining water doesn’t empty toilet bowls and P-traps, which would allow sewer gas to come back up the drain.

But, localized differences in air pressure (“wind”) are able to pass through the vent, which jostles the water in the toilet bowl.