This was a not in service, and not a Mernda or Hurstbridge service.
Clean up after the steam train today?
Yep!
Probably a stupid question, but what is it aiming to clean up?
The steam train today dropped oil and grease on the rails causing havoc with the revenue trains. The Siemens train has wheel sanders and the aim is to restore some traction to the rail head.
That makes sense, after all I think I heard a X’Trap slip a bit when leaving a station right after the steam train went through