the amount of fluid that is in the turkey baster is only a small percentage of the fluid in the entire system. so it will take you a while to replace all the old fluid in the system. it is much easier just to flush the system and get it over with. it only takes about half an hour or less, as opposed to using a turkey baster every other day. but regarding your question, you can remove all the fluid for the reservoir only if you fill it back up before you start turning the steering wheel, the bubbles will just surface in the reservoir.
i know theres the plastic one in the reservoir, but ive never changed any filters when flushing, same for the brakes. just follow the flushing instructions in the fsm, its very short and easy. just make sure you bleed the system well, and have someone help you if if its your first time, someone needs to watch the reservoir.