I'm working on contract basis with an IT giant. Since I have good experience on the project which I'm working now my manager asks me to train the new recruits whenever they join. Giving knowledge transfer (KT) to more than one person is consuming ample amount of my working hours and most of the time I end up working extra hours to compensate the time consumed in KT. Also I never add these working hours ( KT hours ) in my timsheet.

Now, as days goes by my work load is piling up and I'm not able to give my fullest in the project due to these non productive activities. Somebody please tell me a way to work around this situation so that I can politely say or hint my manager that I'm not comfortable on these jobs?