driving UK loco's does anyone know the correct use of the sander option? How should it be used in conjunction with the throttle etc?
Depends on situation more then anything.
Most of the time used when the rail head conditions are poor or due to weather conditions.
Other reasons due to train weight or to avoid wheelspin, as can cause wheel flats or be very distructive to steam locomotive valve gear.
It is also used in WSP (Wheel Slip Protection) on many modern UK trains in case of emergency braking or heavy braking.
i do suggest going over to Rail UK Forums as more people will know the answer.