I would fill it, install the cap, crank up the car and move the wheels from side to side. Suck out the fluid that is now in the reservoir, refill and do it again. I did this about three or four times until what I was removing looked clean. This will allow you to get the fluid out from the hoses, etc.. I would recommend doing it about every 30-40k miles (about the same schedule as brake fluid).
Jim
'85 300D
'95 E320
'97 CRV