Hoping someone can assist - what is the thin tube that runs under the battery tray in my '05 base roadster? Prior owner had a battery leak, battery tray and adjacent fender lining rusting badly. Took it apart, sanded and primed, but in the process this tube (see photo) broke. I cannon figure out what it is - in order to replace it!
Thanks in advance for any assistance.

Pre-breakage (also notice the rust)

Broken tube as it appears to pass through the firewall

At least it's not rusted anymore...