Changing power steering fluid

Reet then. Ma 300tdi's power steering res looks like its been toped up with strawberry milk so im thinking its as old as the Landy. How do you drain the lot before refilling it? I know you can open the bleed nipple but I wasn't convinced that I could run the engine then crank the bleed nipple open to drain it with out causing damage to the pump when it runs dry. Whats the way to go on this one cos I dont want to mix new fluid with my jumbo McStrawberry shake.

the atf in my power steering was that colour from the bottle, or is your mc d's milkshake pink...

Yep. Like nans draylon sofa... a dusty dull pink. Thougt it was suposed to be bright red ATF fluid.