This is pretty straightforward:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=SR&P=41
However, on my car, the recommended ATF has been replaced by Power
Steering Fluid, and who knows if it was done properly?
I read something in a Supra Owner's Group site that if the steering starts
feeling wonky, and there aren't any problems with the rack, that the fluid
needs to be replaced. The instructions are clear, and I have better
instructions from someone who followed the TSRM and came up with a couple
tricks (so you don't have hydraulic fluid spraying all over the place...)
but how can I flush the system and refill with the correct ATF? Should I
just start the flushing process with ATF and continue for an extended
amount of time?