water pump on 2000 Saab 9-3

my question is why is it that every website says that i have to get an additional o ring gasket for the water pump? where do the o-ring gaskets go and why do i need 3 of them? and another thing is do i put gasket sealant on the coolant tube. and how do u suggest i do a coolant flush on a turbo motor?

Asked by for the 2000 Saab 9-3
The water pump is connected to the engine block via a short pipe. The O-rings ned to be of good quality, or else. An egine is flushed when
you have pored water pump into the radiator