Hi Steve,
From your pics in your album your friends appear to have bought a Winsons/Modelworks 5"g GWR 14XX tank loco.
I would have said from one of your pics that the steam oil delivery pipe goes into the main steam pipe in the base of the smokebox, the steam pipe being forward of the blastpipe .
The displacement tank is quite hideous and spoils the loco, and ought to be removed IMHO.
This type of simple displacement lubricator is quite unsuitable for a 5"g loco, and should be replaced anyway.
There must be room for a conventional displacement tank under the cab? In one case I made the rear right hand sand box a displacement tank.
You either need to fit a mechanical lubricator, or a proper hydrostatic sight feed displacement lubricator with a steam feed to the base of the displacement tank via a steam valve on the turret/manifold and an outlet pipe from the top of the tank to the sight glass and then onto the main steam pipe.
The steam oil delivery pipe on your example also looks very small. I use 3/32" dia thinwall copper tube.
Cheers,
Julian