I'm a voulenteer on the mid-hants preserved railway and we wash the locos before they go out in the morning.
Meyshollop
So am I, well, I was until about 2-3 weeks ago, I moved to website work afterwards, I am still working for the railway, but from home at the moment. I should be administrating the MHR Rangers. Oh well. Does Len manage you? Or do you get David (M) instead?
Locos, IIRC, the standard proceedure at the Watercress Line for cleaning was about 1/4 bucket full of parafin, then 2in of cylinder oil, mixed in, then cleaned with some rags and a couple of brushes to get in the small areas.
Smoke boxes are cleaned after every shift, as the loco comes off shed, the fire is also dropped at the same time and the locomotive cab floor washed at the same time.
Tubes are cleaned as and when needed (usually when the loco is out of traffic, I did that a while ago and you are often black when you come out of the smoke box, much to "Rob's" amusement.), boilers were washed once every approximately 6 months, but now Ropley has a reverse isomosis system, its increased greatly. (Basically, pure water.) Brick arches are replaced when needed, usually, when the loco is being examined, if there is damage, its usually reported. Boilers are inspected annually, as most of the other equipment and overhauled once every 10 years.
(sometimes, the boiler has an extension of a year, if it can do a year, then it is a steaming countdown, usually 20 at the highest, but cannot be used afterwards, unless it has been certified and overhauled.)