Windshield washer tee.  This mounts to the underside of the hood on your Omni or Charger (or other L-body car) such as Shelby GLHS (Omni), Charger GLHS, Shelby Charger, Omni GLH Turbo, etc...
 
I haven't seen an NOS Mopar one like this, in like 30yrs.  We only have this one.  Forgot I even had it.
 
That one amazing little touch to your perfect restoration!!