Free space on my jailbroken iOS device is rapidly declining -- how do I figure out why?
This is usually an issue with being unable to properly remove temporary data.

It's root cause could be one of two things:
1. The permissions for the .Trash service is corrupt

Or


There is issues in the directory of the storage component.


Either way the solution is to restore the device and setup as a new iPhone.
Erase all content and settings should work fine too if it wasn't jail broken.

Happy travels!