Hi Garry,
Congrats on some nice finds! Sounds like the Revelation you got is the same model as mine. The attachment you are asking about is a demother. You would connect the hose to the blower end of the cleaner, fill the demother with paradichlorobenzene moth crystals, and connect it to the hose. Then put it in the closet, seal the door, and let it run for about an hour or two.
Glad to hear the hose on yours is well sealed, mine leaks like a sieve! Did you get a full set of attachments with yours? Mine came with everything you see in the pic, except the dust brush, which I picked up later.
Jeff