-Suck reservoir dry. Pull out return line and plug the reservoir hose outlet securely with appropriate means.
-Take the return line and to a container, preferably at least 2-3 litres. You might want to make some kind of hose extension to guide it out of engine bay if there is not enough room beside the engine.
-Fill container with fresh fluid. Jack up the front end of the car. Have a friend who will start the engine and turn steering wheel back and forth while you keep the reservoir topped with fluid. Power steering pump is powerful and will suck reservoir empty in seconds! Make sure you have enough fluid and the reservoir doesn't empty.
With this method I have flushed ps. fluid on my 500 SEC and S8. With the Mercedes I made a huge mess, but with S8 I was more prepared
btw. If I remember correctly, my 1997 PF didn't have a filter. It has the small container.