T. It's the same as loading/unloading or fuelling up (and, with Ctrl, raise/lower a water-scoop in loco's that have one) so it works hard. Most of the time it's pretty foolproof but if you're at a station in a steam route and happen to be by a water crane you might either open the doors or get your tanks topped up so keep an eye on that.
Some of the Armstrong Powerhouse enhanced units have additional controls for DOO (Driver Only Operation) opening either the left or right side independently, to use this you change between DOO or GO (Guard Operated - aka normal TS mode) by pressing Ctrl + R and then to open the doors you press T + U for left or T + O for right, to close the doors you then press R. To see if your set has advanced features you'd need to check with the user manual supplied with that unit.
