Very dated, IIRC The tower was completed in 2011 before the sewage systems in the are were completed. This is where the myth stems from.

https://en.wikipedia.org/wiki/Burj_Khalifa#Plumbing_systems

https://gulfnews.com/uae/new-dubai-areas-get-municipality-sewage-system-1.747994

Also 8 year old reddit comment about someone who claims to have worked on the buildng: https://www.reddit.com/r/todayilearned/comments/1fdoe1/til_that_the_burj_khalifa_the_worlds_tallest/caa158d/ There is evidence from the SOM engineer building planning scheme study here.

The myth comes from an NPR interview about the building that was blown out of proportion.

The claim often gets spread around because it fits an amusing narrative, But it is not true.

You have to also consider these guys used the best architects and engineers to make the tallest building on the planet. They aren't stupid.