Attached is a second David Marcham photo of that train, posted after I sent the photo to you...Paul notes it as a Bogle weed sprayer, and there are a couple of Type 7 / TM-8 tank cars in the consist behind the ISTX car.

Cheers,
Andy L.
Wisconsin

Gents,
Attached is a photo that Paul McCray posted in a Facebook group that I follow.  It shows an 8,000 gallon tank car owned by the Interstate Tank Car Corporation on the Washington & Old Dominion RR in Falls Church, VA sometime after 1956 (when the loco was delivered).  Note the interesting 3-line piping rig that runs along the walkway and up to the dome on either side of the walkway.  It appears to connect to the next car in line via a hose, and there is a fitting at the other end of the car for the same type of connection.  Is this a weed-spray train?  The 1955 ORER shows this as a TM, no special equipment other than heater coils is noted.

Andy L. 
Wisconsin