"That relies on the user have information a PC" ??
A programming track is just a short length of track on a piece of strip wood - so I haven't a clue as to what a working programming track is. The programming track can be taken to the PC.
The advantage of a SPROG is that all settings are saved for each loco. Further each CV is explained in English what it does so all manner of things can be adjusted, such as speed tables and curves very easily.
Far easier than putting numbers into CVs.
XPS is extruded polystyrene as opposed to expanded polystyrene used for disposable cups, packaging etc. This will attack PVC insulation in time.
What you describe as expanded, coming out of a can, is polyurethane foam.
Meths (properly Methylated spirit) is basically Ethanol to which Methanol has been added together with Pyridine (which gives it its purple colour and nasty taste) to prevent it being drunk and so can be sold without any duty being applied.
It smells so that might put you off but it will work. The Meths for Methfix transfers is the same stuff.
If you can get it I would use IPA.
RS do quite a number of three way Toggle switches that look to be what you want. An example is their 734-7050.
You would control operation by suitable use of diodes.
Does the cistern have an isolation valve before the cistern? if so you could close that and then take off the connection to the cistern and then crack the isolation valve to see if any water comes out. If it does then a faulty cistern valve if not it's something else - airlock?
Is it a side entry or bottom entry?
DUDLEY TTR probably means it was made by Thomas Dudley.