Question about steam engine maintenance in the 50's

[Harlesden]

I've been watching this video about the (roughly) fortnightly thorough wash and brush up each steam engine would go through.
What I'm wondering about is after the firebox has been dropped (into an ash pit below the engine) how would the engine then be moved on into the shed where the bulk of maintenance is carried out?
"Wash and Brush Up" 1953 - Trains & British Railways - YouTube
(the firebox is dropped at approximately 5 minutes into the video)

 

[E&W Lucas]

The first part of that film just shows end of day disposal. Take water, empty smokebox, drop fire or clean fire as required, clean out ashpan, refill boiler. Even with a dropped fire, the loco is still in steam, and capable of movement. Obviously, if you're not able to move at the end of the process, you use another loco!

I haven't time to sit through the rest of the film, but it sounds like a description of a " Boiler Washout" and periodic exam.