I need to replace the upholstery tool vacuum hose for my Rug Doctor as it
keeps breaking at flexure points and I keep having to nibble it shorter and
shorter.

Seems like everyone is selling the full attachment while I only need a
length of hose.

It's one inch ID with a steel wire helix which is visible inside. The
helix is strong enough that you can simply twist the entire hose to screw
it into the RD connectors. Looks like the top one here.

http://anver.com/wp-content/uploads/.../ftsvfgrp2.jpg