2011 Forrester has black looking p.s. fluid and I would like to change it. It seems like I could just pull a house and dump it out while not letting the res run dry. Any reason I shouldn't?

Check out this thread: http://www.ultimatesubaru.org/forum/topic/148956-power-steering-flush-procedure/

 

I've done it on both of our Subaru's.  You dont have to start the vehicle.

 

Good luck, it is pretty easy.

Thanks for the link