Kevin's caption (which you have to click on the photo to see) explains it very well:
The crew of WW&F #9 conducts a slightly unorthodox procedure to steam-clean their engine's smokebox. Engineman Rick Sisson works the cleaning procedure on the smokebox, while Fireman J.B. Smith holds a large PVC pipe which directs the effluent away from the locomotive. The material exiting the pipe on the right is a combination of steam and a slurry of soot and cinders. The museum folks refer to the procedure as "sparking."
We joke that the locomotive is blowing its nose.
As far as the jacket - it is a representation of an American Rolled Iron jacket - which was worn by #9 its entire service life. We went through a great deal of research and expense to create it (funded in part by a grant from the National Railway Historical Society.) For all the details on the process, please see
this report.