I have always done it the less messy way... I always suck the p/s fluid out with a turkey baster...then change the filter..

I buy true power steering fluid...valvoline.... it is clear.... I add it back in.. then each week for the next 3 or 4 weeks i repeat the sucking procedure and add new. After about the 4th time, you have a clean system...and you can monitor the system by the "clearness" of the fluid. This takes next to no time.

I usually buy two quarts of fluid.

I tend to do the same with brake fluid in between pad changes... at a pad change, I bleed it down pretty good... brake fluid seems to stay pristine.

No mess, no fuss.

Of course I suck the oil out to change it, rather than draining it.

Tranny fluid, I do the traditional and very messy way... drain the converter and tranny, then drop the pan (the messy part-- and change the filter)

just my .02